Popular Science Monthly/Volume 59/July 1901/The Blue Hill Meteorological Observatory

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METEOROLOGY became established on an independent basis about fifty years ago. With the beginning of a systematic study of the atmospheric conditions there arose a demand for more frequent observations than could be made directly, and, as a result, self-registering meteorological instruments came into use. It was speedily found that the exceedingly sensitive and complicated apparatus necessary for furnishing accurate records of the atmospheric conditions required the services of thoroughly trained and skilful persons in its manipulation. Not only this, but proper exposure of the instruments and careful reduction of their records were necessary. In other words, the generally recognized requirements of a good astronomical observatory must be fulfilled in carrying on the work of a meteorological observatory.

It had long been supposed (and unfortunately is still by many) that any one is competent to make meteorological observations who is able to read a barometer scale or hold a measuring stick in a rainfall basin. The importance of having the instruments automatically record their indications became very generally recognized, if we may judge by the number of self-registering instruments constructed and set in operation, although the considerable cost prevented their general introduction. Then it was that the need for this work of well-trained observers began to be felt. Where meteorology was associated with one of the older physical sciences, such as astronomy, the necessary care was given to the meteorograph; but in most cases, after a brief and generally unsatisfactory trial, the self-recording instruments were kept going in only a perfunctory manner or allowed to fall entirely into disuse. While the necessity for meteorological observations continued, and continuous records became more and more imperatively demanded, yet it was not until the true conditions were fully realized and meteorological observatories comparable with those devoted to astronomical research were built, equipped and manned, that anything like satisfactory atmospheric observations were obtained. Nor was it longer deemed sufficient only to keep up the observation of the meteorological elements; the fact was emphasized that the results must be properly worked up and put into such a form as would best serve the purposes for which they were desired.

Observatories of various degrees of excellence and fitness were established at a number of places, but it was reserved for Professor Heinrich Wild, then director of the Russian Meteorological Service (but now of Zurich), to set us a pattern of what a meteorological observatory should be, in the Pawlowsk Observatory near St. Petersburg.

It has been found by experience that the services of three thoroughly trained and skilled persons are necessary to properly conduct a meteorological observatory. It is the verbal testimony of Dr. Wild that it is better to do entirely without the records of self-registering instruments than to have the records made under the care of untrained and incompetent persons.

A. Lawrence Rotch.

In the United States there long existed an apparent indifference to the demand for numerous continuous atmospheric records, the winds alone receiving the merited attention (except in an experimental way) from our Signal Service organization. A single exception to this indifference was the Central Park Observatory, which was operating unobtrusively along the right lines, but after the stereotyped manner of the older European observatories. For the rest we were mainly content with the observations made at fixed intervals during the day.

Such was the condition of observational meteorology in America at the time when Mr. A. Lawrence Rotch conceived the idea of establishing a meteorological observatory on the Great Blue Hill, near Boston. At first Mr. Rotch intended to use this observatory for special investigations, leaving the regular work to Signal Service observers. As no plan of cooperation with the Signal Service was found feasible, he determined to carry on the entire work under his own direction and at his own expense.

Mr. Rotch was particularly fortunate in his choice of a site for his observatory. Although the summit of the Great Blue Hill is but 635 feet above sea level, yet it possesses many of the characteristics of a mountain. It is the highest point of land in eastern Massachusetts, and offers an unobstructed view for many miles in all directions. This feature has been particularly valuable in prosecuting cloud studies.

The Valley Station of Blue Hill Observatory.

The location is so near the coast that the characteristic water and land influences on the atmospheric conditions can be perceived. Moreover the summit of the hill is near that critical altitude at which the diurnal variation of the wind changes from the low level type to the high altitude type. We had meteorological records from the Signal Service stations on Mt. Washington (altitude about 0,000 feet) and on Pikes Peak (altitude about 14,000 feet), but we had none from the lower altitude at which the powerful local influence of the ground surface ceases to be overpoweringly effective. Thus this observatory fitted into a vacancy which it was desirable to fill. Nor is this all. The wonderful success attending the recent extension of the work of the observatory to the exploration of the upper air by means of-kites has been in no small part due to the perfect adaptation of this locality for carrying on such work. As regards location, the Blue Hill Observatory thus occupies a unique position among the meteorological observatories of the world.

Two secondary stations, at altitudes above the sea of 50 and 200 feet, respectively, at the base of Blue Hill bear the same relation to the main observatory that the base stations bear to the higher ones in the most completely planned European mountain observatory systems; while the Weather Bureau station at Boston and the neighboring Harvard Observatory meteorological station offer the advantages of representing the adjacent country.

Just as Dr. Wild set a pattern for Europeans to copy, so Mr. Rotch has given the United States a model observatory which it will be no mistake to use as a pattern in the future development of observational meteorology in this country. It seems to me that every possible precaution

The Station for Cloud Measurements in Valley, 1896-1897.

has been taken in the placing of the apparatus and in its convenient manipulation. The instruments and apparatus are of good construction and well adapted to the work required. The personnel of the staff could not be improved; certainly not in this country and probably not abroad. The true scientific spirit prevails at the observatory, and I have found there the same distinctive atmosphere which marks the Russian observatory at Pawlowsk. There can. be no doubt but that the Blue Hill Observatory is the most successfully conducted meteorological observatory in America, and its work will compare favorably with that of European observatories of the highest class.

Some may wonder how it was possible for this observatory to have such a good start, reach such a high state of development within a brief space of time, and avoid those errors of organization and management into which much more ambitious institutions had fallen. The reason is very plain to those who are familiar with Mr. Rotch's numerous visits to the best of the European central and mountain observatories. The care that he has taken to inform himself thoroughly in regard to their equipment, work and general effectiveness is clearly reflected in his printed descriptions of these institutions. By this means the youthful director of this new American observatory was enabled to take what might be termed a 'short cut' to leadership in our observational meteorology.

The regular work of the Blue Hill Observatory is carried on by Mr. Rotch with the assistance of Mr. H. H. Clayton, meteorologist, Mr.

The Pole Star recorder for Registered Cloudiness at Night. First Thermograph Lifted by a Kite Employed IN 1894

S. P. Fergusson, mechanician, and Mr. A. E. Sweetland, observer. Not only did Mr. Rotch show excellent judgment in selecting a locality for his observatory, but he has shown equally good judgment in the choice of problems for investigation; he has taken up just those questions concerning which we have been sadly in need of numerical data, and to which every contribution is of distinct value. Moreover Mr. Rotch was exceedingly fortunate in his selection of capable co-workers, for they have responded in a notable manner to the demands which their science has made on them. The investigations undertaken at the observatory may be divided into three classes: (1) The routine work of making observations of the local atmospheric conditions both by automatic registration and direct observation; and the reduction and publication of results. (2) The exploration of upper air by means of kites, and (3) Special studies of important topics by the observatory staff and visiting scientists.

The Blue Hill Observatory was established in 1885. Its report for 1886 shows the institution still in its formation period. The annual report for 1887, when it began to appear regularly in the 'Annals of the Harvard College Observatory,’ is almost complete, lacking only the hourly values of the relative humidity of the atmosphere, but more than making up for this by the very complete hourly record of cloud observations (from 7 a. m. to 11 p. m.). In the report for 1888 all

Record of a Kite Meteorograph.
the usual meteorological elements are given; but thereafter hourly values of the precipitation and cloud observations alone are given, the other elements being recorded only in summary. The reason for this long backward step, for it certainly is such, was probably the desire to economize the time required for reducing the observations and the cost of printing, although it may have been thought that the publication of the hourly observations in extenso during two or three years was sufficient. This latter is not the case, however, for what we most lack in the study of the air conditions in this country is reliable hourly observations conveniently accessible through print. It is especially desirable to have these records when they are as carefully made as those at the Blue Hill Observatory. It must be remarked, however, that the proper reduction of automatic records is a very laborious task.

Starting a Kite Flight on Blue Hill.

Kite Meteorograph in Air.

The successive years of continuous or hourly observations have permitted the determination of the diurnal and annual periods of the chief meteorological elements at the Blue Hill Observatory, summaries of which for several years' averages have been published. The main interest in these results centers in the air movements. The constancy of the local amount of wind from hour to hour has been found to be remarkable, and this, in connection with the variability in the hours of maximum and minimum wind, indicates the nearness to the transition altitude where the lower air conditions change to those of the upper air. These observations of wind velocity, coming in as they do at an intervening altitude between those of the ordinary high exposed surface station and the more elevated mountain stations, permitted the discovery of the gradual shifting towards noon of the hour of minimum diurnal wind velocity, with the gradual increase in altitude. Thus the least wind occurs at Boston at 5 a. m., at Blue Hill at 8 a. m., on the Eiffel Tower at 10 a. m. and shortly after noon on Mt. Washington and other similar high altitudes.

Much of the well-earned reputation of the Blue Hill Observatory depends on the special investigations which have been conducted by its scientific staff. Some of these are the natural concomitants of the peculiar location of the observatory, while others have been taken up on account of their intrinsic importance to meteorological science; still others combine these two features.

Among the questions taken up for the former reason, the following deserve special mention: The investigation of the normal differences of temperature between the base and the summit of the hill, and between the latter and the neighboring Weather Bureau station in Boston; the investigation of the marked inversions of temperature between the base and the summit stations; experiments on the electrical condition of the atmosphere; and studies of the vertical component of the wind as measured at the observatory.

The Blue Hill series of observations of visibility of more or less distant hills and mountains is very important, although the positive deductions as yet made from the data assembled in regard to this phenomenon are very meager. In general, however, it was found that the summer haze about balanced the winter fogs, so that an annual periodicity is but slightly marked. The diurnal period is also not clearly pronounced.

The location of the Blue Hill Observatory also made it a very desirable place at which to undertake open air experiments on the absolute and relative accuracy of anemometers. These were very much needed in view of the fact that the old errors of observed wind velocities could no longer be neglected when the comparatively recent quantitative study of the winds was widely taken up; and since much of the

Modified Hargrave Kite.

Fergusson's Kite Meteorograph.

investigation designed to remedy this defect has been performed under artificial indoor conditions. These Blue Hill investigations showed plainly the necessity for greater uniformity in anemometers both as regards shape and size. The fan or bladed anemometers, with the use of ball bearings, seem to have many advantages over the ordinary cup anemometers now so generally used. There was found to be still much room for improvement in the pressure wind gauges, as those at present in use are not thoroughly satisfactory. The pressure tube anemometers, upon which many hopes have been built, showed need of some further modifications before it will be perfectly adapted to all conditions of wind and weather. Concerning the standardizing and testing of anemometers under artificial conditions, the opinion is advanced that a current of air produced by a blower is more likely to give absolute results than the whirling machine at present in use.

Among the important general meteorological questions taken up are the following: (1) The investigation of the temperature indications of thermometers placed in different kinds of thermometer shelters or screens. (2) The study of special phenomena exhibited by the records of self-registering meteorological instruments; such, for instance, as the dynamic effect of the wind on barograph records. (3) The study of weather predictions, from both the central and local points of view, and the demonstration that the combination of the two methods gave the best results. (4) The study of sudden falls of temperature and their relation to general atmospheric conditions. (5) The study of wave-like oscillations shown in the records of barometric pressures. (6) Studies concerning the periodicity of the weather. (7) The discussion of cloud observations, especially those made at the Blue Hill Observatory. (8) The improvement of meteorological apparatus, especially in the self-registering devices, and adapting the existing instruments to special needs. (9) The study of special cloud forms. (10) Cooperative study of clouds during the International 'Cloud year.'

That the movements of the atmosphere follow on certain laws we all recognize. Some of these laws we know, others remain still to be discovered. No work of the Blue Hill Observatory has exceeded in importance its studies of the actually observed movements of the air, and the so-called dynamic changes which these movements cause the air to undergo. In nearly every phase of this many-sided question this observatory has increased our stock of knowledge.

The study of the upper atmosphere was early begun by the staff of the Blue Hill Observatory, At first it was mainly carried on by means of cloud observations, but since 1894 by means of registering meteorological instruments carried aloft by kites. To this observatory belongs the honor of thus sending up into the air the first continuously recording meteorological instruments used in this manner. Mr. Eddy, of New Jersey, used his kites in making this first trial. The work has been pushed with such success that records of atmospheric pressure, temperature, relative humidity and wind velocity have been secured by means of kites up to a height of 15,800 feet above the sea.

In a pioneer work of this kind, it was found necessary not only to modify old apparatus and methods so as to fit the novel applications, but also to devise new ones as well; and many of the details of the system as established at Blue Hill have been copied by meteorologists in the prosecution of similar researches both in this country and in Europe.

In this connection the Blue Hill studies of the clouds have led to the consideration of many problems to which these phenomena either directly or indirectly furnish a key. As in other studies carried on there, this work has been undertaken in the light of what has been done by other investigators; and in Mr. Clayton's report on the subject an excellent summary of what has already been accomplished introduces us to the more distinctively Blue Hill work. It has too frequently happened

Evolution of the Kite Reel.

that the cloud work which has been done in different parts of the world has had its value much decreased owing to uncertainties in cloud nomenclature, and much of the recognized value of the Blue Hill work is to be attributed to the great care exercised in this preliminary matter. A valuable contribution has been made to the revision of cloud nomenclature, taking into account the elevations of the clouds. The annual and diurnal periodicity of clouds has been carefully studied on the basis of cloudiness at different levels.

In the study of the relation of clouds to rainfall are taken up: clouds preceding rain, clouds between intervals of rain and clouds following rain. The methods and cause of cloud formation were also carefully considered. The most important part of this special investigation is the use to which the cloud observations are put in the study of atmospheric dynamics, taking up in succession the questions: the relation of clouds to cyclones and anti-cyclones, having regard to the altitudes of the cloud levels; the annual and diurnal periods in the winds in general, at various levels as shown by direct observation near the ground and extended upwards to high altitudes by means of the observed cloud movements; the wind movements in cyclones and anti-cyclones from the ground up to the altitude of the highest clouds; the relation of the direction of the cirrus clouds to the existing temperature gradient; the relation between the velocity of storms, and the consequent variability of the weather, to the general movement of the atmosphere as shown by surface wind and cloud observations; the use of cloud observations in weather forecasts; and the frequency of winds from various directions at different heights above the ground, for different hours of the day, shown by wind and cloud observations.

The work of making observations of the atmospheric conditions in the free air by means of kites has been carried out with the success achieved only by the persistent endeavors of the observatory staff, not only in overcoming the difficulties in the mechanical construction of the apparatus employed, but also in the actual work of kite flying.

Experiments were undertaken as to the best forms of kites to use, the best materials for their construction, and the best lines to use for flying them. Special forms of self-recording meteorological instruments had to be so designed or so changed as to be adapted to the demands of kite work. Great care was exercised in so exposing the instruments that their possible errors would be reduced to a minimum. During the year 1897 there were thirty-eight successful kite flights, in 1898 thirty-five, in 1899 twenty-five, and in 1900 twenty-four; the average height above sea level at which records were obtained during the respective years being 7,350 feet, 7,400 feet and 8,450 feet, thus showing constant improvement in the methods employed.

The discussion of the Blue Hill observations has added very materially to our still meager knowledge of the distribution of the meteorological elements in the free air, and their variation with change in altitude. The average increase of wind velocities with increasing altitude was determined chiefly for those altitudes for which we have the fewest data because it is so difficult to make measurements there by means of the clouds. The change in direction of air currents at different levels was also clearly and accurately brought out by the changes in position of the kites as they ascended and descended. Such data as these are particularly valuable for determining the effects of the friction of the ground on the winds, and for testing quantitatively the theories of the air circulation which have heretofore depended mainly on qualitative generalities.

The decrease (and in the abnormal cases, the increase) in temperature with height above the ground has been carefully studied, and especially in the various phases which occur under different typical atmospheric conditions. The diurnal changes of temperature at different altitudes have been also carefully studied. The determination of the numerical values of these elements is very important in helping to complete the theories of the atmospheric circulation, solar insolation, and the transference of heat from the earth to the air.

The rate of change of relative humidity with change of altitude, due to vertical change of temperature, is very important in connection with the calculation of the heights of clouds by computing the altitude of the dew point temperature under known conditions near the ground; and the Blue Hill observations not only offer data for increasing the accuracy of these calculations, but also a criterion for testing their absolute accuracy.

Until 1886 the only weather map in the United States was printed at the Chief Signal Office in Washington, but in May of that year Mr. Rotch with the assistance of Mr. Cole, the government observer in Boston, began to chart the 7 a. m. reports that were received there, and manifolded the map by the cyclostyle process. This was the origin of the daily weather map that is now issued in great numbers from many of the Weather Bureau Stations throughout the United States.

From 1887 until 1891 local weather forecasts were furnished by the Blue Hill Observatory to the Boston press and announced from the observatory by the display of weather signals. These weather predictions were undoubtedly a considerable improvement over those made in Washington, which depended on the weather map alone, especially for the twenty-four hours immediately succeeding the time of observation, and the demonstration of this, in direct competition with the Weather Bureau predictions, probably had some effect in causing the government service to appoint local forecast officials to supplement the general predictions made at Washington. It must be borne in mind in this connection, that this combined method of making weather predictions has been, in a measure, practically carried out in European countries ever since an international telegraphic exchange of weather observations went into effect. In this country, however, we had learned to rely too much on the general predictions issued from Washington.

There can be no doubt that the work of the Blue Hill Observatory has had a very great quickening influence in the recent developments in observational meteorology in this country. Not only has its thoroughly independent attitude and scientific spirit enabled it to make usefulness and not policy its watchword, but it has also permitted it to improve the older traditions of American meteorology, by adding to them the best features of European meteorology.

So far as concerns the regular routine work of observation of the purely local atmospheric conditions made at the Blue Hill Observatory, it is impossible to realize its importance to American meteorology under the light of present conditions alone. One must go back twenty years to the conditions existing in the early eighties to properly appreciate its innovating character. Concerning the extra routine work, such as the studies of the upper air conditions and their application to atmospheric mechanics, no comment seems necessary further than to mention the fact that this work occupies a prominent position in the front line of scientific advance in this direction. We have had a recent example of this in the discoveries attending Mr. Clayton's studies of eclipse meteorology, in which important extensions of Ferrels' cold centered cyclone have in all likelihood been made which will greatly aid in the solution of some hitherto unexplained meteorological problems.

The importance attached by scientists to the work of the Blue Hill Observatory is plainly indicated by the numerous long and appreciative reviews and notices of this work which have appeared in such general scientific journals as 'Nature' and 'Science,' and such special journals as the 'Meteorologische Zeitschrift' and the 'American Meteorological Journal.' Probably not one of the long list of reports and other publications of the observatory has been passed by without printed comment, and frequently a single paper has called forth several reviews. Moreover the confidence with which this work has been received is shown by the fact that the results have been freely used by subsequent investigators.

It is a noteworthy fact that by taking the initiative in the systematic sounding or exploration of the upper air by means of kites, the Blue Hill Observatory has added one more feature to the already long list of American pioneer contributions to meteorology, among which may be mentioned, Loomis' storm and weather maps, Espy's dynamical theories, Ferrels' theories of the atmospheric circulation, and the more complete extension of the application of weather knowledge to practical affairs by the Signal Service and Weather Bureau.

The official publications of the observatory are: the earlier annual reports published separately and the later ones published since 1887 in the 'Annals of the Observatory of Harvard College,' special memoirs and discussions forming an important feature of these reports; monthly and annual summaries of the climatic observations, which were manifolded and distributed locally up to 1896, and some of which the 'U. S. Monthly Weather Review' and the monthly report of the New England section still publish; occasional Bulletins containing original memoirs that it was desired to publish promptly, on special meteorological topics.

In addition to the preparation of these official reports, the members of the observatory staff have published a great number of letters, articles, and reports in the journals of general and technical science both in Europe and America. This individually published material has always been of that high character which bears internal evidence of the earnestness and ability of the authors, and it has always received from scientists both at home and abroad the careful consideration due it.

The high character of the work undertaken and the great amount accomplished by steady application during the fifteen years of its continuance have given the Blue Hill Observatory a position among the best observatories of the world. There are certainly very few even of the great national meteorological observatories which are better known or are held in higher esteem than the private observatory established and maintained by Mr. Rotch on the highest summit of the Blue Hills of Milton.

In closing this article I venture to express the opinion that when the history of meteorology during the latter part of the nineteenth century is written, the Blue Hill Observatory will be assigned the foremost place in American observational meteorology, and this judgment will be based not only on the observations which have been made, but also on their proper discussion and correlation with allied branches of this science of the atmosphere.