to bring the eyepiece in the most convenient and comfortable position for observation, the telescope being supported in any suitable manner as by means of a sleeve 35 mounted 5on the bracket 34.
Any suitable mechanical expedient may be employed for mounting, within the lower end of the telescope, the bi-prism P3 and the telescope objective L2.
10Slidably mounted within the outer sleeve of the telescope is a sleeve 36 in which is fixed the wave length wedge W, said sleeve being provided with a finger piece 37 which projects through an elongated slot in the outer 15sleeve 36. The outer sleeve is provided with a fixed scale, indicated at 38, graduated to indicate wave lengths, and a pointer or index 39 movable with the inner sleeve, cooperates with said scale to indicate the 20wave length of the particular light ray brought into coincidence with the ocular slit, S2 for any particular position of the sleeve 36 and wedge W.
For convenience in making readings, a 25reflecting mirror 40 may be mounted on the upper side of the telescope so that the observer may make the readings indicated by the scale 38 and index 39 without having to change his position. A similar reflecting 30mirror 41 is preferably provided for the photometer scale, which mirror may be secured midway of a rod 42 extending Between the side walls 11a, 11b, of the lamp supporting bracket. A magnifying lens 43 may also be 35provided between the photometer scale 29 and the mirror 41 to enable the readings of the photometer settings to be made more easily. In order to shield the eyes of the observer from the direct rays from the lamp 40L, I prefer to place a shield 45 in front of said lamp. As shown, the side walls 11a, 11a are provided with grooves 46, in which the shield 45 is mounted slidably and detachably, said shield being provided with: apertures 4547 to permit the passage to the prism P1 of the beams of light. reflected. by the surfaces R1, R2.
If the sample is of very low reflective power, or if it is desired to obtain a finer 50comparison, a revolving sector 48 may be interposed in the beam from the surface R1 of the comparison standard, and between such surface and the ray directing prisim P1. As shown in Figs. 6 and 7 I provide a 55standard 49, said standard being adapted to support the small electric motor 50, to the armature shaft of which the sector 48 is secured. Any suitable means may be employed to move the sector into and out of the path of 60the beam from the surface R2, as shown the sector is detachably secured to the motor shaft by the knurled lock nut 51. The sector is preferably constructed so that the readings of the photometer scale when the sector is 65used will represent one-tenth of the indicated values so that when the sector is used micrometric readings may be made directly from said scale. A second standard 52 may also be provided from the side of the collimator opposite to the standard 49 so that a testing70 sector may be used for testing the instrument.
For the purpose of investigating or comparing the transmissive properties of substances, as for example liqueds I provide a75 pair of standards 53, 54 adapted to support the containers for such substances in the path of the beams from the surfaces R1, R2, respectively; any suitable containers, such as vials or tubes having glass or other 80transparent stoppers may be provided for holding liquids. When transmissive properties are to be investigated, magnesium carbonate will ordinarily be employed for both of the reflecting surfaces.85
It will be seen that an instrument constructed in accordance with the principles hereinbefore described is exceptionally simple; the movement of the photometer lamp is positive and the position of said lamp with90 respect to the reflecting surfaces R1, R2, provides an accurate means for determining the reflective power of such surfaces according to the well known law of the squares of the distances between the lamp and surfaces,95 The manufacture of a scale to indicate directly the value of such squares is comparatively simple and inexpensive, and as the scale and its index are at all times fixed relatively to the members whose position they100 indicate, without requiring the interposition of any moving mechanical parts between such members and the indicating means, all error's due to the use of such moving parts are avoided. Obviously any suitable means105 may be employed for varying the relative positions of the lamp and reflecting surfaces, and as the readings depend on the positions of these parts and not on the means for moving them, no great amount of accuracy is110 required in the machining or construction of such means.
The same is also true with respect to the spectrometer, it being obvious that the movement of the wedge is positive and direct,115 and that the wave length scale and index are positively located and fixed. with respect to the members whose position they indicate. As the sleeve 86 which carries the wedge is of considerable length the amount of error120 caused by tilting of the sleeve due to lost motion between it and the sleeve, obviously would be negligible.
In Figs. 8 to 11 inclusive a slightly different constructional example for the 125spectrometer is shown; the principle of maintaining a fixed relationship between collimator, dispersion prism, and telescope having a fixed ocular aperture being the. same as shown and described in connection with130