Journal of the Optical Society of America/Volume 30/Issue 12/Proceedings of the Twenty-Fifth Annual Meeting

Proceedings of the Twenty-Fifth Annual Meeting of the Optical Society of America

Rochester, New York, October 3-5, 1940

Iwas particularly appropriate that the twenty-fifth annual meeting should have been held in Rochester, the birthplace of the Society. For several years before the founding of the Optical Society of America in 1916, a local group of optical experts had been organized, and the national society grew out of this organization. During the process, the local group maintained its identity and is known today as the Rochester Section. The enthusiastic efforts of the local committee appointed by the Rochester section were largely responsible for making this meeting one of the most successful in the history of the Society.

The meeting was opened Thursday, October 3, at 9:30 a.m. by President Gibson with a session of contributed papers.

Evening Lecture

A lecture and demonstration of practical uses of the academically familiar phenomena of polarization by Mr. Edwin H. Land delighted those who knew what to expect as much as those who really preferred to believe in magic. For the latter, a sheet of ordinary-looking celluloid held in the hand could be black, white, red, or green at Mr. Land’s whim. At the same time and in the same place could be seen a picture of the Taj Mahal or the kitchen sink depending upon the manner of holding the sheet material before the eyes.

For the more technically minded, the importance of this demonstration resided in the fact that only one projection lantern was used. This is made possible by controlling the degree of polarization of a polarizing surface in which the pictures are formed. A transparent sheet composed of oriented molecules of a long chain polymer is brought into contact with a solution containing a component which, when combined with the original molecule, produces a polarizing molecule. By controlling the number of these polarizing molecules, it is possible to achieve any desired degree of contrast in an image in terms of polarization if the image is viewed through a polarizing material. The advantages of projecting three-dimensional pictures by means of a single lantern are many. This was admirably demonstrated by a series of stereoscopic pictures representing subjects of all types. The demonstration closed with a stereoscopic picture projected in full color by means of a single lantern.

Symposium of Invited Papers on the Progress in American Optical Science and Industry

If for no other reason, the Rochester meeting would be memorable for its group of invited papers. These were presented by authors who combined unquestioned knowledge of their fields with the happy faculty of discussing, their subjects in an extremely lucid manner. The program of these papers was as follows:

1. A Quarter Century of Optics Reviewed, Herbert E. Ives, Bell Telephone Laboratories.

2. Quality Control in the Manufacture of Optical Instruments—Twenty-Five Years’ Progress, W. W. Graeper, Bausch & Lomb Optical Company.

3. Recent Developments in Photography, C. E. K. Mees}, Eastman Kodak Company.

4. Producing Low Reflecting Glass, C. Hawley Cartwright, Corning Glass Works.

Dr. Ives began by describing the transformation undergone by the concept of radiation from the time of Newton to the present. His discussion fascinated the imagination of the theorists as completely as it did those who think of radio as something to hear with and light as something to see with. In a most entertaining manner, he described the upset of the well-ordered wave theory after the discovery of the photoelectric effect and the resulting transformation of the subject into a paradise for the mathematician.

Physiological optics was represented by the speaker as a subject of slow and labored progress, which is still open to further chemical and physical interpretation. Helmholtz’ theory of the visual purple and the theory of the visual violet, although attacked through a “clam’s eye view,” have been extended to the vertebrates. An inter-national dispute has arisen out of the question whether the vitamin-deficient see “redder” than the well-fed people of America.

Developments in optical apparatus were found to be responsible for much of the progress during the last quarter-century. The controlled manufacture of ruled gratings, the discovery of supersonic gratings, the Schmidt camera, and aspheric lenses were given special mention.

Great advances in the measurement and specification of color have resulted from the development of photoelectric spectrophotometers and the concurrent development of a standard trilinear coordinate system. In the practical field, fluorescent lighting, photographic flash lamps, phototelegraphy, television, and the electron microscope are the most recent contributions of optics.

Advancement in science depends upon the perfection of the tools with which it works. Mr. Graeper assigned a large part of this responsibility in the optical industry to the methods of inspection employed by the optical instrument manufacturers.

Availability of materials, of course, is another factor in production, especially of those materials which are artificially producible. In this connection, the recent discovery of a deposit of a high quality calcite in one of our southwestern states is particularly interesting. The fact that methods of manufacture in the last twenty-five years have culminated in a perfection of manufacturing techniques which equal the best inspection methods, may be regarded as both a challenge to inspection methods and a tribute to the quality control in manufacture.

Dr. Mees began his talk by comparing the size and weight of the equipment needed by the photographer in 1900 to that which he carries in 1940. The most important developments in photography during the last twenty-five years have been brought about through the cooperative efforts of physicists and chemists, but they have been made commercially possible because of the increased popular interest in photography. The things the amateur wanted were pictures easier to make, pictures in motion, and pictures in color. The technical developments which have fulfilled these wishes are: (1) improved methods of the optical sensitizing of emulsions; (2) the development of mechanized reversal processing; (3) the introduction of elaborate miniature cameras of high mechanical quality; and (4) the introduction of the integral tripack systems of color photography.

The improved methods of optical sensitizing arose from the development of the polymethine dyes, in which two nuclei are connected by a chain of methine groups. The absorption and sensitizing spectra of these dyes depend upon the length of the chain and the weight of the nuclei. The new dyes increase the sensitivity of slow, fine-grain emulsions more than they do that of high speed emulsions; and this makes it possible to prepare films of satisfactory speed having an image structure which allows a considerable degree of enlargement. This development has greatly encouraged the use of miniature cameras.

The growth of amateur cinematography has been dependent upon the excellent results obtained by reversal processing carried out on conntinuous developing machines using automatic compensation for the second exposure.

On the optical side, the growth of amateur cinematography and of miniature cameras has led to the introduction of lenses of very much higher aperture than those used previously, and this has been assisted by the introduction of improved glasses, particularly glasses of low dispersion and high refractive index.

The use of the integral tripack has been very successful in color photography, and the majority of all substandard motion pictures are now made in color. In other branches of photography, the use of color processes is constantly increasing.

To make things disappear was once a conjuror’s trick, but Dr. Cartwright demonstrated for his audience that optical advancement has made this magic possible without legerdemain. Glass is visible because of the light it reflects; it becomes invisible when it is sufficiently transparent.

H. Dennis Taylor in 1892 observed that camera lenses were “faster” after they became tarnished. Several methods for artificially tarnishing glass were subsequently developed. A more physical approach to the problem was made in 1936 by J. Strong, who evaporated films of CaF₂, and realized the value of a film material having an index of refraction intermediate between that of air and the glass. In 1938, K. Blodgett showed that the thickness of the film was of paramount importance and succeeded in reducing the reflection of monochromatic light to zero by the application of “skeletonized” films of metallic stearates. In 1938, Cartwright and Turner applied evaporated films of the metallic fluorides to glass under conditions which satisfied the correct index and thickness requirements. The metallic fluorides have unusually low indices of refraction, and a satisfactory result for photography is obtained by their approach to the ideal index. The correct thickness of the film is obtained by observing the reflection of light during the condensation of the metallic fluorides.

Although the thickness can be correct for only one wave-length of light, reflection is greatly reduced throughout the entire visible spectrum. Metallic fluoride films can be made sufficiently rugged for camera lenses and the reduced reflections from the six to ten air-glass surfaces noticeably increase the speed. The perfection of a camera lens is further increased by the absence of flare and ghost images that normally appear under adverse lighting conditions.

Dr. Cartwright projected an interesting series of “before and after” pictures, all of which demonstrated the increase in image sharpness and contrast. Perhaps the most striking of these were the photographs taken with the coronograph of Professor D. Menzel.

Annual Dinner and First Award of the Adolph Lomb Medal

On Friday evening, members of the Society and their wives were the guests of the Bausch & Lomb Optical Company at a dinner held at the Oak Hill Country Club. Nearly four hundred were in attendance. The toastmaster, Mr. C. S. Hallauer, first called on Mr. Carl Bausch, who told of the measures instituted by his company to supply the increasing need for optical glass and optical parts during this active period of preparation for national defense. The toastmaster then called on President Gibson, who introduced the charter members of the Society in turn. He also read letters from several charter members who were unable to be present because of illness.

Dr. W. B. Rayton was then asked to recount for the benefit of new members the events that led to the formation of the Optical Society of America. From his various anecdotes relating to the early days, it was abundantly evident that considerable growth and progress has been made during the quarter-century. He paid special tribute to Mr. Adolph Lomb, a charter member and treasurer of the Society until his death in 1932.

President Gibson then explained the purpose of the Board of Directors in establishing the Adolph Lomb Medal and read the conditions of award adopted at the Board meeting in October, 1939. Past President R. C. Gibbs, the chairman of the committee to nominate a candidate to receive the first award then spoke as follows:

“After canvassing a representative group of members of the Society for suggestions of suitable nominees and after a careful study of the scientific achievements of the various persons on the list thus assembled, the committee made a unanimous nomination for an award. This nomination was transmitted to the Board of Directors, which, by a unanimous vote on March 2, 1940, officially awarded the Adolph Lomb Medal for 1940 to David Lewis MacAdam.

“Born in Philadelphia, July 1, 1910, Dr. MacAdam attended the public schools in Upper Darby, Pennsylvania, and Lehigh University, receiving the B.S. degree from the latter in 1932. He then spent four years in graduate study at the Massachusetts Institute of Technology, where he received the Ph.D. degree in 1936. Since that time he has been a member of the staff of the Physics Department of the Research Laboratories at the Eastman Kodak Company in Rochester, New York.

“Dr. MacAdam’s scientific contributions have been embodied in twenty-one published papers or reports. A survey of these contributions shows five studies of major importance which may be considered as the bases for this award.

“1. Dr. MacAdam developed the theory of the maximum visual efficiency of colored materials and, on the basis of appropriate computations, prepared tables showing the maximum visual efficiency as a function of excitation purity for
David L. MacAdamtwenty-four dominant wave-lengths. He studied and examined the general type of spectrophotometric curve which yields a maximum value for the visual efficiency for materials exhibiting a given chromaticity when illuminated with light of a specified quality, and presented a new proof of the validity and uniqueness of this type of curve.

“2. In a study of ‘Photometric Relationships Between Complementary Colors,’ he presented formulas and tables for the interconversion of colorimetric and excitation purities, and reviewed the complementary relations between colors having maximum visual efficiencies.

“3. In a review of the ‘Photographic Aspects of the Theory of Three-Color Reproduction,’ he examined the significance of the concept of photographic spectral sensitivity and emphasized the desirability of emulsions having contrast independent of wave-length. He also determined the limits within which it is possible or desirable to increase purity by an increase of contrast.

“4. In a report on ‘Subtractive Color Mixture and Color Reproduction’ he showed how the analytical form of a simple rule for predicting the colors of mixtures of certain dyes can be incorporated into the theory of color reproduction, and derived formulas for use in printing a subtractive reproduction, and in the simultaneous introduction of partially negative spectral sensitivities.

“5. More recently he has undertaken to investigate the ‘Noticeability of Color Difference in Daylight’ which has now culminated in a report presented at this meeting of the Society. He has developed and carried out an extensive series of color-match observations and has examined in detail the probable errors to be expected and encountered in such color matching.

“Mr. President: It gives me great pleasure, on behalf of the Committee and of the officers of the Society, to present at this time Dr. David Lewis MacAdam as a person highly qualified to receive the Adolph Lomb Medal because of his noteworthy contributions to optics.”’ After President Gibson had formally bestowed the medal, Dr. MacAdam responded briefly as follows:

“Mr. President: I realize that I must not take the time that would be necessary to express adequately my appreciation of the award which you have just bestowed upon me. May I say simply that I feel greatly honored at being chosen to receive the first award of this symbol of encouragement for young men entering the field of optics. I thank you sincerely.”

Business Session

A brief business session of the Society was held Saturday morning, October 5, at 9:45 A.M., President Gibson presiding. Formal reports of the Secretary, Treasurer, and Editor of Publications for the calendar year 1939^[1] were received and placed on file. Informal reports covering the period from January 1, 1940 to the time of the annual meeting in 1940 were also presented.

President Gibson called attention to the fact that the term of appointment of Arthur C. Hardy as Secretary of the Society would expire at this annual meeting. He also called attention to the report of a Nominating Committee, which had been circulated in accordance with the provisions of the By-Laws. On a motion from the floor which was carried unanimously, the President was instructed to cast one ballot for Arthur C. Hardy. He thereupon declared Arthur C. Hardy elected Secretary for the term October, 1940 to October, 1941.

The President called attention also to the unusually fine program that had been arranged for this meeting and declared his intention to dispatch letters of appreciation to those who had been responsible for the arrangements. By a motion which was carried unanimously, the President was instructed to send telegrams expressing regrets to the charter members who had been unable to attend the meeting.

Contributed Papers

Sessions for the reading and discussion of contributed papers continued throughout Saturday, October 5, the authors’ abstracts of these papers being appended.

Registration

The total number of members who registered at this meeting was 208. Much of the success of the meeting was due to the efforts of a committee appointed by the Rochester Section and consisting of the following: Leon V. Foster, Chairman, R. E. Burroughs, A. A. Cook, A. Doyle, George Gardner, H. F. Kurtz, R. Miller, B. Noyes, Brian O’Brien, F. H. Perrin, C. M. Tuttle, and T. R. Wilkins.

Among the special events arranged by this committee were trips to the Research Laboratories of the Eastman Kodak Company, to the Bausch & Lomb Optical Company, and to many other places of interest. A complimentary luncheon at the Taylor Instrument Company on Friday was followed by an inspection tour of the plant. An unusually attractive program for the entertainment of the ladies was arranged by a committee under the chairmanship of Mrs. Brian O’Brien.

Meeting of the Board of Directors

A meeting of the Board of Directors was held on Wednesday, October 2, 1940. Minutes of the meeting are appended.

Arthur C. Hardy, Secretary

Minutes of the Sixteenth Meeting of the Board of Directors of the Optical Society of America, Incorporated

Hotel Sagamore, Rochester, New York, October 2, 1940

BESIDES the transaction of routine business and the receiving of reports from chairmen of committees and representatives, the following items of general interest to members of the Society were taken up.

Announcement by Secretary

Results of Letter Ballots

1. Award of first Adolph Lomb Medal to David L. MacAdam.

2. Appointment of Clifton M. Tuttle as a member of the Committee on Meetings and Programs.

3. Appointment of (Mrs.) Blanche Bellamy to the Colorimetry Committee.

4. Resolution setting time and place of next O. S. A. meeting (to be held jointly with the American Physical Society in Cambridge, Massachusetts, February 21 and 22, 1941).

5. Appointment of Special Committee to Cooperate with A. I. P. in planning the Tenth Anniversary Meeting of the Founder Societies in October, 1941.

Membership

The Secretary reported that since the last meeting of the Board four members had died, forty-two new members had been elected as of January 1, 1940, and eight as of January 1, 1941.

Transfer from Associate to Regular Membership

The following were transferred from associate to regular membership:

Frederick W. Brock	1194
Willoughby M. Cady	1191
H. Keffer Hartline	1210
F. C. Hutchings	1026
Edwin E. Jelley	1230
Theodore F. Karwoski	1217
C. N. Nelson	1231
Robert H. Park	1219
Earle E. Richardson	1232
Charles P. Shillaber	1244
John Spence	1188
J. A. Van den Akker	1242
George Wald	1208
S. Rains Wallace	1226

Financial Status of the Society

The Treasurer gave an informal report which showed that the financial condition of the Society continued satisfactory.

Election of Editor

George R. Harrison was unanimously elected Editor of the Journal for the term October, 1940, to October, 1944.

Committee Appointments

To Consider and Report Upon New Contract with the American Institute of Physics:

F. C. Gibbs, Chairman
L. B. Tuckerman	H. F. Kurtz

To Report at the February, 1941 meeting on the possibility of awarding an Adolph Lomb Medal in October, 1942:

W. B. Rayton, Chairman,
R. C. Gibbs	Selig Hecht
G. R. Harrison	F. L. Mohler

To report at the February, 1941 meeting on the possibility of awarding an Ives Medal in 1941:

Rudolf Kingslake, Chairman
Jesse W. Beams	P. E. Klopsteg
H. E. Ives	A. G. Worthing

Emeritus Membership

On the basis of a report submitted by a Committee Appointed to Consider the Matter of Emeritus Memberships, it was voted to amend Article I of the By-Laws as follows:

By inserting in Section 1, Classes of Membership: the word “Emeritus.”

By inserting after the third paragraph of Section 3, Eligibility: the paragraph:

“Any person who has retired from active work, has reached the age of 65 years, and has been a member for at least 20 years is eligible for emeritus membership. Other members may, by a two-thirds (2/3) vote of the Board of Directors, be declared eligible for emeritus membership.”

By inserting after the fourth paragraph of Section 5, Election to Membership: the paragraph:

“Any eligible member may, at his own request, be transferred to emeritus membership by the Secretary.”

And by inserting after the second paragraph of Section 6, Duties and Privileges: the paragraph:

“Emeritus members shall have all of the privileges of their former membership status, except the right to receive the Journal and other publications of the Society.”

A.I.P. Representative

Arthur C. Hardy was nominated to succeed himself as O. S. A. representative on the Governing Board of the American Institute of Physics.

Arthur C. Hardy, Secretary

Program of Sessions

(Titles and Abstracts of Papers)

1. Refractive Indices of Liquid Aliphatic Organic Compounds. Maurice L. Huggins, Research Laboratories, Eastman Kodak Co.

The molal refraction, defined by a Gladstone-Dale type of equation, R=V(n_D-1), where V is the molal volume and n_D is the refractive index for the Na D lines, is, for a normal paraffin, a rectilinear function of the chain length. For any paraffin, the molal refraction is, practically within experimental error, the sum of “bond refractions,” each of which has a magnitude depending on the kinds of atom (hydrogen; primary, secondary, tertiary or quaternary carbon) joined by the bond. The molal refraction of an unsaturated aliphatic hydrocarbon can be computed from that for the corresponding saturated compound by subtracting a characteristic constant for each double or triple bond (the size of the constant depending somewhat on the number of R groups attached to the multiply bonded atoms) and adding another constant if two multiple bonds are adjacent to or conjugated with each other. The molal refraction of many derivatives of aliphatic hydrocarbons can be computed quite accurately by adding appropriate constants, characteristic of the substituting atoms or groups, to the refractions calculated for the corresponding unsubstituted compounds. Constants have been derived for chlorides, bromides, iodides, amines, alcohols, ketones, aldehydes, acids, esters, ethers, thio-ethers, etc. Equations are presented for the calculation, for compounds of the various classes discussed, of molal refractions from the structural formulas.

2. The Regulation of Tungsten and Mercury Lamps. Harold Stewart, University of Rochester.

Certain radiometric problems attempted here have required the regulation of high intensity tungsten lamps and of mercury arc lamps. Voltage, current, resistance, radiation, and power d.c. regulators were developed for tungsten lamps. Voltage regulation was chosen. A 1500-watt 115volt tungsten lamp in series with a resistance bank of heater coils is connected to the 220-volt line. In parallel with the resistance bank are six power tubes. Differences in the lamp voltage from a reference voltage are put into a two-stage d.c. amplifier and the output is applied to the grids of the power tubes in such a way as to increase the power tube current when the lamp voltage decreases. Fluctuations in the voltage output of the local generator are several percent, but regulation of lamp voltage is about 1/400 of one percent. However the radiation output of the lamps is not better than 1/10 of one percent due to several causes within the lamp itself. The radiation output of the type H5 mercury arc lamps has been regulated to better than 1/10 of one percent for short periods (30 minutes) by a photoelectric regulator. Six power tubes are connected in parallel with the lamp across the secondary of the lamp’s transformer. Light from the lamp falls on a photo-cell in series with 100 megohms which operates into a one-stage feed-back amplifier. The output of the feedback amplifier goes to the input of a three-stage d.c. amplifier the output of which controls the voltage on the grids of the power tubes in such a way as to decrease the current in the power tubes when the photo-current decreases. Without the regulator, radiation fluctuations are several percent. When the regulator is to be used for long periods a thermopile or other such device is used as a reference standard.

3. Factors Contributing to the Discrepancy Between Subjective and Skiascopic Determinations of the Refraction of the Eye.^[2] Glenn A. Fry, Ohio State University.

Bibliography: J. P. C. Southall, “Optical principles of skiametry,” J. Opt. Soc. Am. 13, 245-266 (1928).

An eye can be rendered artificially emmetropic by placing before it an ophthalmic lens which corrects the spherical and astigmatic errors of refraction. When such an eye is subjected to skiascopic examination at a distance of, say, 40 cm, the eye can be made to fixate a target in the same plane as the skiascope, and although the subject reports that the target is seen clearly, the skiascope will indicate that the eye is under-accommodated. Conceivably, the following factors might contribute to this discrepancy between subjective and skiascopic criteria of the state of refraction: (1) displacement of the skiascope from the line of sight; (2) the lazy lag of accommodation; (3) spherical aberration; (4) chromatic aberration. The paper reports an investigation of the relative roles played by these factors. A special type of skiascope and an instrument called an aberrometer have been designed for carrying out the investigation. These two instruments make it possible to evaluate the roles played by the different factors. The displacement of the skiascope from the line of sight was not found to be an important factor, and the discrepancy between the subjective and skiascopic determinations of the eye involves to a certain extent all the other factors mentioned above.

4. Ophthalmic Lens Testing Instrument. A. Ames, Jr. and Kenneth N. Ogle,^[3] Dartmouth Medical School.

In the study of the importance of the relative sizes and shapes of the ocular images in the two eyes to binocular vision, it is necessary to have an instrument with which the optical properties of lenses, as used with the eyes, can be completely determined. Since no existing instrument was adaptable, this necessitated the building of one. The present paper briefly describes the instrument from the point of view of measuring power, astigmatism, peripheral aberrations, prismatic deviation, magnification and distortion for the lens used with the stationary and mobile eye. An example of the measurements is given. (There are two such instruments at the present time—one at Dartmouth, Department of Research in Physiological Optics, and the second at the American Optical Company in Southbridge, Massachusetts.)

Bibliography: A. Ames, Jr., G. H. Gliddon and K. N. Ogle, ”Size and shape of ocular images. I. Methods of determination and physiologic significance,” Arch. Ophth 7, 576-597 (April, 1932); A. Ames, Jr., K. N. Ogle and G. Gliddon, “Corresponding retinal points, the horopter and size and shape of ocular images,” J. Opt. Soc. Am. 22, 614 (1932); K. N. Ogle, “The correction of aniseikonia with ophthalmic lenses," J. Opt. Soc. Am. 26, 323 (1936); E. H. Carleton and L. F. Madigan, “Relationships between aniseikonia and ametropia,” Arch. Ophth. 18, 237-247 (August, 1937).

5. Photographic Analysis of Some Unexplored Visual Phenomena. William A. Gardner, Columbia University. If an observer fixate a stationary point along the track of a speeding automobile, he will apparently see the spokes of the rotating wheels. This effect has been tentatively ascribed to stroboscopic vision, or to subjective factors. Photographs (with camera speed slow, relative to automobile velocity) show this same effect, proving that it depends on objective factors. Experiments reveal that apparent spoke visibility is limited to the lower hemisphere, that the eye must rigorously fixate a nearby stationary point, and that the effect is independent of velocity, lighting, or angle of vision. Photographs, exactly duplicating the visual impressions, are obtained by keeping the camera shutter wide open during the transit of the experimental wheel. Analysis shows that this effect depends entirely on mechanics. The apparent “spokes” are, in reality, the locus of maximum overlap (and therefore of maximum brightness) of the cycloids formed by the combined rotation and translation of each spoke. The summation of these cycloids forms a static pattern (progressively created by the combined rotation and translation of the wheel), which glides across the sentient retina or the sensitive film. Instead of demanding a stroboscopic theory of vision, therefore, this “cycloid effect” favors a theory of continuity of vision analogous to the continuous sensitivity of the camera film with wide-open shutter. A comparable illusion was described in 1821, whereby the spokes of a rapidly rolling carriage wheel, when viewed through a series of fixed vertical slits, appeared curved. Roget, in 1824, explained this effect as due to mechanical factors, and showed that the same phenomenon could be produced by a stationary rotating wheel when viewed through a transversely moving system of slits. This “Roget effect” is experimentally duplicated, and seen as a startling fixed pattern of variably curved vertical lines. Photographs made with wide-open camera shutter produce an image identical with that seen by the eye. The “cycloid effect” and the “Roget effect” are examples of the manner in which both eye and camera build up, by a summation of mechanically produced images, a retinal (or optical) pattern, which has wholly objective causality, but wholly subjective (or photographic) existence.

Bibliography: P. F. Gaehr, Science 68, 567 (1928); R. M. Packard, Science 68, 567-568 (1928); C. E. Ferree, Science 68, 645-646 (1928); J. P. Guilford, J. Exp. Psychol. 12, 259-266 (1929); H. S. Gradle, Science 68, 404 (1928); “J. M.,” Quarterly Journal of Science, Literature, and the Arts 10, 282 (1821); P. M. Roget, Phil. Trans. Roy. Soc. London 1, 131 (1825). Cited by Helmholtz, Physiological Optic (Optical Society of America), Vol. 2, p. 223.

6. A Supersonic Cell Fluorometer. H. B. Briggs, Bell Telephone Laboratories.

A method will be described for the measurement of the rise and decay of luminescence in phosphors excited by cathode-ray beams. It is particularly suited to the investigation of phosphors classed as fast, i.e., those in which the major changes in intensity occur in a few microseconds. The problem is to measure the intensity of the emitted light at definite time intervals after the excitation has started or stopped, and during periods sufficiently short so that no major changes in intensity occur within the measuring interval. This is accomplished by utilizing the properties of a supersonic cell arranged to produce the Debye-Sears diffraction effect. The high speed shutter action is obtained by modulating the supersonic wave train to produce short steep sided pulses. Time intervals in the decay process are measured in terms of distances traversed by the sound waves in water. Light intensities sufficient for direct measurement in terms of photoelectric cell response are obtained by synchronizing the periodic excitation of the phosphor with the diffracting wave pulses in the liquid. The phase relation between the excitation of the phosphor and the diffracting wave pulses may be continuously varied by moving the supersonic cell to increase or decrease the distance from the quartz crystal generating the sound waves to the section of the liquid traversed by the light beam. Several methods of using the device will be described, and some results obtained by these methods will be shown.

7. Interference Phenomena with a Moving Medium.^[4] Herbert E. Ives AND G. R. Stillwell, Bell Telephone Laboratories.

An experimental study of interference patterns set up on a mercury surface when the source of ripples is in motion with respect to the surface. Ripples are produced by air jets interrupted by sector disks in the air supply, and the ripple patterns, or the standing wave patterns, are photographed by intermittent and steady illumination. The air jets, light source and camera are arranged on a lathe bed so as to move with velocities which are a large fraction of the ripple velocity. The Fresnel biprism is simulated by two jets, and it is shown that the interference pattern with a moving medium is altered from that for a stationary medium in a manner which is corrected by the Fitzgerald contraction and the Larmor-Lorentz change of frequency. Stationary interference phenomena produced by the simultaneous occurrence of both capillary and gravity waves of different velocities are shown to call for the Fresnel drag coefficient to nullify effects of motion of the medium. The amplitudes of the “biprism’’ or double jet interference fringes are unaltered by motion of the medium. The question of the rate of, flow of energy in front of and behind a moving source is discussed.

Symposium of Invited Papers

Progress in American Optical Science and Industry

8. A Quarter Century of Optics Reviewed. Herbert E. Ives, Bell Telephone Laboratories.

9. Quality Control in the Manufacture of Optical Instruments—Twenty-five Years’ Progress. W. W. Graeper, Bausch & Lomb Optical Company.

10. Recent Developments in Photography. C. E. K. Mees, Eastman Kodak Company.

11. Producing Low Reflecting Glass. C. Hawley Cartwright, Corning Glass Works.

12. Changes in Lens Characteristics with Temperature. A. Francis Turner, Bausch & Lomb Optical Co.

The calculation of the change of correction of a lens with temperature requires, besides data on the coefficient of expansion of the metal of the mount, also a knowledge of the coefficient of expansion of the glass, together with its temperature variation of index and dispersion. Measured data on glass for low temperatures are lacking. Using published^[5] results obtained above room temperature one calculates, for instance, a decrease in focal length in a simple imaging system of a few hundredths percent per 50°C decrease in temperature. Although such temperature effects are small, they cannot always be ignored in the design of optical instruments, as for use in airplanes where -40°C may be encountered. A need is felt by the industry for more low temperature data on optical glasses.

13. Chemical Methods for Increasing the Transparency of Glass Surfaces. Frank L. Jones and Howard J. Homer,^[6] Mellon Institute.

The amount of light transmitted by a lens or prism can be increased by suitable chemical treatment of the polished surface. The effect was described by Taylor in 1892, Kollmorgen in 1916, and Wright in 1921. The general use of treated lenses was delayed because of a lack of knowledge of the physical and chemical principles involved in the process. The chemical treatment involves the formation of a transparent surface film of silica by the removal of the higher refractive index oxides to a depth approximately equal to one-fourth the wave-length of the light for which maximum transmission is desired. Such removal is possible without damage to the surface polish if the solvent does not dissolve silica. The surface film is not noticeably different from the base glass in hardness. The gain in light transmission and the decrease in surface reflection is slightly less than that produced by evaporated films of materials of lower refractive index than silica. Solvents that will remove higher refractive index materials from a glass surface include water, fused salts, alkaline phosphate solutions, salt solutions and acid solutions. A dilute acid solution such as 1 percent nitric acid is suitable for most optical glasses with the exception of crown glass. The treatment time is short for glasses containing large amounts of lead or barium and long for borosilicate glasses. The solution speed for a given glass approximately doubles for each 10°C rise in temperature. Freshly prepared glass surfaces react with the solution at a uniform rate that depends on the glass composition, the solution composition, and the temperature. When a silica surface film has been formed, it may be processed in various ways that will render the surface unreactive so that a second treatment will not appreciably change the thickness of the film. Glass surfaces not freshly prepared are usually unevenly reactive due to accidental stabilizing of the surface by' handling or processing.

14. An Automatic Telescope Control. Arthur C. Hardy, Massachusetts Institute of Technology.

During the progress of some tests on the flatness of window glass, it became desirable to determine the deviation experienced by a small parallel bundle of rays traversing the glass normally to its surface. Measuring this deviation by means of a collimator and telescope is unsatisfactory because modern drawn glass is of such high quality that the maximum deviation is usually less than a few minutes of arc. It would, therefore, be necessary to use a telescope having an entrance pupil of such size as to mask the local variations in the deviation over the glass surface. This problem was satisfactorily solved by using a photoelectric cell to control the telescope. Light from a tungsten lamp enters a collimator whose slit is replaced by a circular aperture. At the image of this aperture, where cross-hairs would normally be located, there is a sort of photometric field consisting of two pieces of Polaroid placed side by side with their axes at right angles. Behind this photometric field is a single piece of Polaroid which is rotated in its own plane at a rate of thirty revolutions per second. When the image of the circular diaphragm is exactly centered on the dividing line of the photometric field, the rotation of the second Polaroid produces no variation in the light flux transmitted by the system. If the image is decentered, a sixty-cycle current is produced in the output circuit of an amplifier actuated by a photoelectric cell, the phase of the current depending upon which half of the photometric field receives the greater amount of light. This current is used to operate a motor in a manner previously described.^[7] The motor drives a tangent screw which controls the telescope and another screw which controls a recording pen. As a piece of glass is moved through the beam, a record is made on an adding machine tape six inches in width. The advantage of this method is due chiefly to the fact that the telescope is not required to have a resolving power as high as the angular deviation which it measures. This comes about because the photoelectric cell is able, with this arrangement, to determine very accurately when the diffraction pattern produced by the objective has been bisected by the dividing line of the photometric field. The telescope objective used in these tests had a focal length of one meter, and it was fitted in most cases with a diaphragm having a circular aperture only 0.1 inch in diameter. The uncertainty in the setting was of the order of ±2 seconds. This optical system could readily be adapted to such purposes as the guiding of an astronomical telescope or the recording of galvanometer deflections.

15. Optical Properties of Evaporated and of Burnished Vitreous Quartz in the Extreme Ultraviolet. Richard Tousey, Tufts College.

The specular reflectivities of quartz evaporated onto crystalline and onto vitreous quartz, and of burnished (slowly polished) vitreous quartz have been measured at 45°, 60°, 75°, and 85° incidence within the wave-length range 910A to 1436A. Values of refractive index and extinction coefficient have been computed from these reflectivities^[8]. These results will be compared with similar data for crystalline quartz and for vitreous quartz etched in KOH^[9], which, having almost no surface layer, are as near “ideal” surfaces as possible. These data indicate that a burnished surface of vitreous quartz does not closely resemble an ideal surface of either crystalline or vitreous quartz, while one produced by evaporation is very unlike either ideal surface. The strong selective reflection at 1190A and the weaker one at 1070A, characteristic of both crystalline and etched vitreous quartz, are greatly reduced for vitreous quartz by burnishing the surface. The extinction coefficient curve for a typical burnished surface is fairly smooth, with the hump at 1190A only one-third as high as for etched vitreous quartz. The surface produced by evaporation shows practically no selective reflection at all whether condensed on crystalline or vitreous quartz. The extinction coefficient for evaporated quartz rises rapidly from near zero at 1436A to a value of 0.6 at 1216A. From this wave-length to 1026A it runs practically constant. As a check on this work and on the reflection method for determining the extinction coefficient, the transmission values of an evaporated surface of quartz have been measured directly to 1100A by using LiF as a support. These are in agreement with the extinction coefficient curve as determined by reflection.

16. Measurement of Numerical Aperture. R. Bruce Horsfall, Jr., Bausch & Lomb Optical Company.

The customary definition of numerical aperture is adequate, and techniques of measurement are well known in the case of well corrected systems such as microscope objectives. In dealing with uncorrected or poorly corrected lenses such as condensers, there are deficiencies which may lead to misunderstanding and disagreement. Techniques of measurement approximating conditions of most frequent use are recommended as standards. It is suggested that condensers be tested by comparison with objectives of known N.A., using an unrestricted source for uncorrected condensers and a source which will just fill the objective field for corrected condensers. Mention is made of the term “Aplanatic Aperture” used by Carpenter-Dallinger^[10] and a suggested revision of definition is proposed.

17. An Improved Radiation Pyrometer.^[11] T. R. Harrison and Wm. H. Wannamaker, The Brown Instrument Company.

In the development of a new radiation pyrometer, the following characteristics were required: (1) constancy of calibration with different distance-to-target diameter ratios up to twenty to one; (2) freedom from ambient temperature errors; (3) freedom from transient errors while ambient temperature is changing; (4) reasonably high electromotive force; (5) practically complete response within from two to four seconds. The thermoelectric type was found to be the most adaptable and dependable for general use. Consideration of ambient temperature effects, which is of much importance in modern industrial practice, was carried out by aid of mathematical analysis. In one assumed case, with a very sensitive type of thermopile losing heat from its hot junction by radiation alone, it is shown that an increase in operating ambient temperature of 180°F (from 80°F to 260°F) results in a drop in output voltage of 38 percent for a constant furnace temperature of 1300°F. The corresponding error in reading is 315°F. At a furnace temperature of 3000°F the decrease in voltage is 17 percent and the error in reading is 387°F. Under similar conditions with a less sensitive thermopile having a conduction factor of 3×10¹⁰, this 180°F increase in operating ambient temperature would result in a decrease in output voltage of from 12.2 percent to 12.5 percent for any furnace temperature between the two values mentioned. The error in reading would range from 58°F to 162°F over the stated span of furnace temperatures. The constancy of ratio of e.m.f.’s with the latter case makes that case suitable for compensation by means of a nickel wire shunt connected across the thermopile terminals. This method was adopted. Other methods of compensation are considered. Test data show the degree of perfection realized in the various respects indicated. Special features of construction are shown, rendering the pyrometer practically free from the usual transient errors accompanying changes in the temperature of the pyrometer. All of the thermopile junctions are spot-welded and the construction is arranged throughout to withstand high ambient temperatures.

18. Calibration Data on General Electric Recording Spectrophotometer. J. L. Michaelson and W. R. Fanter, General Electric Company.

Due to the general interest shown by members of the Optical Society of America in spectrophotometry, it has occurred to the authors that it would be interesting to present calibration data obtained from various General Electric spectrophotometers. Therefore, during the past two years we have recorded rather complete data on the performance of these instruments, which will be presented.

Bibliography: A. C. Hardy, J. Opt. Soc. Am. and Rev. Sci. Inst. 18, 96 (1929). J. L. Michaelson, J. Opt. Soc. Am. 28, 365 (1938). Orrin W. Pineo, J. Opt. Soc. Am. 30, 276 (1940).

19. The Importance of Optically Clean Absorption Cells in the Determination of the Concentration of Dye Solutions. S. Q. Duntley, Massachusetts Institute of Technology.

Spectrophotometric transmission data are often used in determining the strength of dye solutions. Customarily, effects due to the presence of the absorption cell and to the solvent are compensated by placing a duplicate cell filled with undyed solvent in the comparison beam of the photometer. It is the purpose of this paper to investigate the errors in dye strength determinations which may result when this compensation is imperfect. Such imperfect compensation may occur during a series of measurements due to contamination of the outer cell surfaces by fingerprints, spilled dye solution, etc. By the application of differential calculus to Beer’s law, it can be shown that the greatest change in transmission for a given percentage change in dye concentration occurs when the transmission is 37 percent. It can further be shown that the errors arising from imperfect cell compensation can be slightly reduced by using a lower value of transmission. However, it is never possible to reduce the error to negligible proportions by this device. For example, with a pair of cells which, when filled with solvent, yield an apparent transmission factor of 99 percent, the resulting error in ∆C/C is greater than 50 percent even when the sample transmits no more than 15 percent. This leads to the conclusion that the use of concentrated solutions does not excuse the operator from checking the condition of his cells before each measurement. The treatment is extended to show the effect of imperfect cell compensation on data taken with the “five times,” cam available for the Hardy recording spectrophotometer.

20. The Viewing Angle of Reflectometry. Elliot Q. Adams, Lamp Development Laboratory, General Electric Company, Nela Park.

Many instruments for the rapid measurement of the reflectance of matte surfaces provide for illumination, or viewing, at an angle of 45°, although it has been known for some time that the angle of equivalence with diffuse illumination is, for most matte surfaces, appreciably greater than 45°. Thus A. H. Taylor and C. H. Sharp, in discussing^[12] the Taylor absolute reflectometer, speak of viewing at 50°, while McNicholas^[13] reports; “Thus for matt samples of the kind herein studied (of not extremely low reflectance), one would be quite safe in choosing an angle of observation of 55° and assuming an accuracy of 1 or 2 percent.” It appears not to have been pointed out that there is a priori reason for illuminating at an angle of approximately this value: If diffuse illumination is to be replaced by illumination from a finite number of points, the nearest equivalence will be secured by locating the sources at the corners of a regular polyhedron, i.e., of a regular tetrahedron, octahedron or cube, the number of sources being, respectively, 4, 6 and 8. For an opaque plane surface, the sources behind the plane will not contribute to the illumination, hence may be omitted. If the remaining sources are so located as to make equal angles with the normal to the surface, and if the reflectance of the surface does not vary with azimuth, the normal brightness will, by symmetry, be unchanged if the 2, 3 or 4 sources are replaced by a single source of the total luminous intensity, at the location of one of them. The angle from the normal will be, in each case, that between the threefold and fourfold axes in the cubic crystallographic system. This angle is tan^-1${\sqrt {2}}=$54°44′8+″. To the degree of accuracy of the reciprocity principle, the apparent reflectance will be the same for normal illumination and viewing at an angle of 54'44’8",

21. An Extreme Case of the Performance of the Eye versus that of the Spectrophotometer.^[14] I. H. Godlove, E. I. duPont de Nemours and Company.

The addition of small amounts of Crocein Scarlet to Tartrazine was supposed by Draves^[15] to be a case where the eye can detect smaller additions than a spectrophotometer; but it was shown by Nutting,^[16] using the Hardy spectrophotometer,^[17] that the reverse is true if the measurements are not confined to a single wave-length, as was done by Draves. This case is one in which the two spectral absorption curves involved are very different in shape. The opposite extreme, where the curves have similar shapes, includes cases where, at least under industrial working conditions, the spectrophotometer cannot detect as small additions as the eye. This extreme is illustrated by mixtures of Pontacyl Carmines 2B and 6B Conc., which are not chemically identical but have very similar spectral absorption curves. For equal weights of standardized dyes, the long wave portions of the curves for the solutions can be practically superimposed, the short wave portions being parallel; somewhat different relations hold for the reflection curves of dyeings. Two very experienced dye testers find that 2.5 percent of the latter dye mixed with the former can be seen to change the color of the skeins, but the mixture would usually be passed as not “off-shade,” while a 5 percent admixture would cause positive rejection. Using the curves of the buffered solutions of the two dyes normally employed by us for spectrophotometric standardization, the hue change due to a 25 percent admixture of the latter dye probably can be detected by inspection of the curves; but the curve due to a 10 percent admixture (with 90 percent of the 2B type) is so close to that of the former unmixed dye that, when the two curves are drawn by the fountain pen of the Hardy-G. E. instrument,^[18] they overlap too much to be separated. Making computations on the ICI system of colorimetric specification, the 10 percent addition is found to cause a change of about 0.0014, 0.0004 and 0.0017 in the x, y and Y values, respectively. These values were obtained when all errors due to weighing and hygroscopicity of samples and to making up solutions were eliminated; some other errors were eliminated by reading directly on the instrument counter at selected wavelengths. If these differences are considered as errors due to a single impurity of known character, and the indicated precautions are taken, then the performance of the instrument, using solutions, becomes comparable to that of the eye, using dyed skeins. But these conditions are ones which cannot be used in routine standardization. In particular, the number and nature of the impurities are often unknown and variable; also, it is inconvenient to eliminate errors by measurements on the standard every time the corresponding lot comes up, or by reading on the counter. The time element, as well as serious difficulties of “levelness” and incompleteness of “exhaust,” makes measurements on skeins or pieces wholly impracticable; but measurements of this sort will be reported. It is our experience that the majority of cases fall between the two extremes discussed; but enough fall near the “similar-curve” extreme to make standardization “for shade” (chromaticity) frequently very unsatisfactory when compared to standardization by “dye testing.”

22. Noticeability of Color Difference in Daylight. David L. MacAdam, Eastman Kodak Company.

The probable error of two component additive visual color matching has been adopted as the most reproducible criterion of the noticeability of color differences. The probable errors of matching a series of colors are proportional to the corresponding just noticeable differences, within the rather great uncertainties of the latter. An apparatus has been employed in which the color of each half of a two-degree circular field can be varied corresponding to the points along any of a very great number of straight lines in the chromaticity diagram. The luminance of each half of the test field remains constant for all of the additive mixtures of the light from any two of a set of over one hundred color filters, all of which have equal luminous transmittances for the quality of light incident upon them in the instrument. A surrounding field of forty degrees diameter can be uniformly illuminated to any desired luminance and chromaticity. Over 18,000 color matches have been made by one observer, with 15 millilamberts luminance in the test field and 7.5 millilamberts of daylight quality (ICI illuminant C) in the surrounding field. The probable errors of determination of position along specified straight lines in the chromaticity diagram can be shown as functions of the positions on those lines corresponding to the chromaticities of the colors matched. The probable errors of purity determinations for representative dominant wave-lengths and their complementaries (including purples) reveal a direct relation between the noticeabilities of purity differences for nearly neutral complementary chromaticities. The noticeabilities of chromaticity differences along straight lines close to the spectrum locus and the boundary of the purples are very simple functions of distance along those lines. A curve for the probable error of wave-length matching under conditions of automatically constant luminance of the spectrum has been deduced from the observed data and shows only two minima, at about 486 mμ and 582 mμ. The probable errors of matching white (illuminant C) with mixtures of complementary colors can be represented by points on an ellipse around the point representing white in the chromaticity diagram. Similar ellipses represent the observed probable errors of all kinds of two-color mixtures matching eighteen other chromaticities well distributed over the chromaticity diagram. The major characteristics of all of the curves and loci representing the results for the principal observer have been confirmed by less extensive series of color matches by other observers.

23. X—Z Planes in the 1931 ICI System of Colorimetry. Elliot Q. Adams, Lamp Development Laboratory, General Electric Company, Nela Park.

The Maxwell triangle usual in colorimetry is predicated on a symmetrical relationship among the three components of the Young-Helmholtz theory. There is no reason to treat them symmetrically; the Munsell color system is one of cylindrical coordinates about the axis of value, the 1931 ICI system attaches all the luminosity to the Y component, and observations of chromaticity differences are made after equating brightness. By plotting X and Z values for colors of the same luminous reflectance (albedo, Munsell value) it is found that a suitably chosen ratio of scales (threefold greater for X) gives a nearly uniform radial and circumferential spacing of the Munsell colors, centered about the neutral color of equal value. For measurements made under ICI standard illuminant C (as were those of Glenn and Killian) normalization by division by (respectively) X and Z for standard illuminant C gives X_e. and Z_e1, and a scale-factor of approximately $\scriptstyle {2{\frac {1}{2}}}$. Plotting Z_e-Y against X_e-Y brings the neutral color for each value of luminous reflectance to the origin of coordinates. Approximate register of colors of equal hue and chroma, and unequal value, is obtained by converting X_e1, Y₁, and Z_e to V_x, V_x1 V_y1 using the Munsell-Sloan-Godlove value function, and plotting V_z-V_y against V_x-V_y. These subtractions are the mathematical representation of inhibitory nervous connections (synapses) in the retina, according to the author’s theory of color vision.

Bibliography: E. Q. Adams and P. W. Cobb, J. Exp. Psych. 5, 39 (1922). E. Q. Adams, J. Opt. Soc. Am. 6, 932 (1922); Psych. Rev. 30, 56 (1923). D. B. Judd, J. Opt. Soc. Am. 23, 359 (1933). ‘A. E. O.Munsell, L. L. Sloan and I. H. Godlove, J. Opt. Soc. Am. 23, 394, 419 (1933), D. Nickerson, ‘‘Use of I.C.I. tristimulus values in disk colorimetry,” U. S. Department of Agriculture (1938). W. D. Wright, Nature 146, 155 (1940).

24. Change of Color with Change of Particle Size.^[19] I. H. Godlove, E. I. duPont de Nemours and Company.

The previously developed theories^[20] of the change in the three attributes of surface color, which accompany a change in size of pigment particles, have been elaborated and corrected, and have been tested by application to a great many cases observed in the laboratory and found in the literature. Excellent agreement of the theory with the facts is found. The chief color changes are: (1) the increase in lightness due to decreased absorption by particles of decreasing size; (2) the dulling due to the greater surface reflection of light not absorbed; and (3) certain hue changes predictable from the changes with increased subdivision of particles, or with decreased thickness of absorbing layer, known to occur in the absorption or transmission curves of solutions of corresponding color. The hue changes are describable as those resulting from the assumption that most of the reflected light from pigment surfaces is due to light transmitted through the particles; and they are in the direction corresponding to decreased absorption in the wave-length region of the characteristic maximum absorption, as the particle size decreases. It is further found that, roughly speaking, subdivision of the particles has the same effect on the hue as admixture of black or white pigment to the chromatic one, or changing from oil film or wet pigment to dry powder in air, except that, especially on addition of certain white pigments, a blue-violet component due to scattering of light by very small particles is blended with the main component of the reflected light.

25. A New Polarimeter Using Sheet Polarizing Elements. Roger S. Estey, Spencer Lens Company.

A new polarimeter will be described which employs Polaroid material in the polarizer and analyzer. A narrow strip is superimposed on a large disk of this material to form a three-part field in the polarizer. This, like the Lippich half-shade device, can be set to a selected sensitivity and can be used with light of any wave-length. The analyzer contains a disk of Polaroid material which is mounted in a cone bearing and is controlled by a worm gear and worm. The position of the analyzer can be read to 0.1 degree by reference to a graduated drum on the worm shaft. Sample tubes 200 mm long and shorter can be accommodated. In an instrument of this grade, sheet polarizing material offers many advantages. The end point device is simple, easy to mount and to adjust. The glass plates between which the Polaroid sheeting is laminated serve also as splash plates. In the material selected, the polarization is practically complete through the middle of the visible spectrum and is still adequate near the limits of visibility. If one attempts to match the fields when the instrument is illuminated with white light a residual color difference is evident. Because of the rotatory dispersion of the sample it is useless to attempt measurements under these conditions with any polarimeter. When the instrument is used with monochromatic light these color differences disappear. The use of an orange filter to modify the light from a tungsten lamp is common practice with simple polarimeters designed primarily to measure glucose and albumen in urine. In this application the rotatory dispersion has a small effect on the color of the field because the total rotation is so small (5°-10°). Nevertheless it is desirable to supply a filter which will control the wave-length limits of the transmitted band with sufficient accuracy to ensure that measurements made with this illumination will have the same values as reference measurements made with sodium light. A similar problem arises with filters designed to approximate the effect of other wave-lengths. Data on such filters will be presented.

Index to Authors

Adams, Elliot Q.—Nos. 20 and 23

Ames, A., Jr. and Kenneth N. Ogle—No. 4

Briggs, H. B.—No. 6

Cartwright, C. Hawley—No. 11

Duntley, S. Q.—No. 19

Estey, Roger S.—No. 25

Fanter, W. R.—see Michaelson, J. L.

Fry, Glenn A.—No. 3

Gardner, William A.—No. 5

Godlove, I. H.—Nos. 21 and 24

Graeper, W. W.—No. 9

Hardy, Arthur C.—No. 14

Harrison, T. R. and Wm. H. Wannamaker—No. 17

Homer, Howard J.—see Jones, Frank L.

Horsfall, R. Bruce, Jr.—No. 16

Huggins, Maurice L.—No. 1

Ives, Herbert E.—No. 8

Ives, Herbert E. and G. R. Stilwell—No. 7

Jones, Frank L. and Howard J. Homer—No. 13

MacAdam, David L.—No. 22

Mees, C. E. K.—No. 10

Michaelson, J. L. and W. R. Fanter—No. 18

Ogle, Kenneth N.—see Ames, A., Jr.

Stewart, Harold—No. 2

Stilwell, G. R.—see Ives, Herbert E.

Tousey, Richard—No. 15

Turner, A. Francis—No. 12

Wannamaker, Wm. H.—see Harrison, T. R.

1. Published in the J. Opt. Soc. Am. 30, 259-264 (1940).
2. To be submitted to J.O.S.A.
3. Presented by Mr. Ogle.
4. The present paper will appear in full in J. Opt. Soc. Am.
5. E.g., Int. Crit. Tab. Vol. 1.
6. Bausch & Lomb Optical Company’s Industrial Fellowship, Mellon Institute.
7. A. C. Hardy, J. Opt. Soc. Am. and Rev. Sci. Inst. 18, 109 (1929).
8. R. Tousey, J. Opt. Soc. Am. 29, 235 (1939).
9. Lord Rayleigh, Proc. Roy. Soc. 160, 507 (1937). R. Tousey, Phys. Rev. 57, 29A, 1060 (1940).
10. C. B. Carpenter, revised by W. H. Dallinger, “The Microscope and its Revelations,” eighth edition, pp. 307-315.
11. The present paper will appear in full in Rev. Sci. Inst.
12. A. H. Taylor and C. H. Sharp, Trans. Ill. Eng. Soc. 15, 811 (1920).
13. H. J. McNicholas, Bur. Stand. J. Research I, 29 (1928).
14. The present paper will appear in full in J. Opt. Soc. Am.
15. C. Z. Draves, J.Opt. Soc. Am. 21, 336-46 (1931).
16. R. D. Nutting, J.Opt. Soc. Am. 24, 135-8 1929).
17. A. C. Hardy,J. Opt. Soc. Am. 18, 96-117 (1929).
18. A. C. Hardy,J.Opt. Soc. Am. 25, 305-11 (1935), J. L. Michaelson, J. Opt. Soc. Am. 28, 365- 71 (1938).
19. The present paper will appear in full in J. Opt. Soc. Am.
20. Merwin, Proc. Am. Soc. Test. Mat. 17 (ii), 404-830 (1917).