proceedings: philosophical society 333 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 738th meeting was held on March 14, 1914, at the Cosmos Club, 

 President Fischer in the chair; 60 persons present. 



The evening was devoted to a symposium on photography. Mr. 

 E. D. TiLLYER spoke on Photographic lenses and plates. He discussed 

 the old and new types of glass used for lenses and described briefly the 

 methods of correcting for spherical aberration, coma, astigmatism, curva- 

 ture of field, distorsion, and chromatic aberration. Various types and 

 combinations of photographic lenses were illustrated by lantern slides. 

 Requirements of plates for different purposes as regards emulsion, rapid- 

 it}'-, and grain were cUscussed. Paper was discussed by Mr. Humphreys. 



Mr. K. Burns spoke on Astronomical photography and the Schumann 

 region. The Schumann region is so-called because before his investi- 

 gations observations could not be made in regions where wave lengths 

 are less than 1800 Angstrom units. For astronomical use plates must 

 usually be rapid at low intensities. The application of refractors and 

 reflectors to astronomical photography was discussed at length and 

 lantern slides shown of instruments and photographs of interesting 

 celestial regions. For wide fi«lds the refractor is limited by the coma. 

 The paper was chscussed by Messrs. Rines and Humphreys, particularly 

 as to photographs giving details of planetary surface markings. 



Mr. F. E. Wright presented a paper on Color photography and illus- 

 trated his paper by some excellent specimens of this work. Color pho- 

 tography is based on Helmholz's trichromatic theory. Present practical 

 methods are three: By taking three exposures simultaneously through 

 three films, one red, one blue, and one green, and superimposing the three 

 negatives by use of prisms; by use of screen ruled alternately with red, 

 green, and blue lines about ^J-q inch apart; and Lumiere's method by use 

 of very small starch grains dyed red, green, and blue and mixed together 

 and mounted on back of sensitized plate, the back being placed next the 

 lens when photograph is taken. The slides exhibited were taken by the 

 second method. The paper was discussed b,y Messrs. Bauer, Priest, 

 TiLLYER, and Humphreys. At 10:05 the meeting adjourned. 



The 739th meeting was held on March 28, 1914, at the Cosmos Club, 

 President Fischer in the chair; 36 persons present. 



Mr. R. Y. Ferner presented a paper on A reasonable performance of a 

 high grade watch . He outlined the methods of tests used in four prominent 

 foreign observatories and gave the criterions and tolerances by which the 

 performances of watches under test are judged. It was pointed out that 

 for the determination of the true quality of the position adjustment of a 

 watch it is desirable to eliminate, bj^ the method of test, the gradual 

 progressive change of rate which is evident in practicall}^ all watches. 

 Lantern slides giving curves of results of isochronism tests were shown, 

 and the desirability of this test pointed out. An outline of the test which 

 will be applied to watches at the Bureau of Standards was then shown, 

 together Avith the tolerances which have been adopted for the granting of 



