Septejibee 20, 1895.] 



SCIENCE. 



351 



calls body colors (Korperfarben) due to 

 chemical modification of the reflecting sur- 

 face. "While it is abundantly possible 

 that coloi'ed illumination upon suitable 

 color-receptive materials can give rise to 

 similar body colors, we are still far from 

 having these materials under control. There 

 seems at present to be greater promise in a 

 second and quite different application of 

 optical principles, that of taking three 

 separate negatives simultaneously from the 

 same object through color screens appro- 

 priately chosen in accordance with the 

 Helmholtz theory of color. The positives 

 from these, taken on suitably dyed plates, 

 are then superposed; or light transmitted 

 through the negatives is combined by an 

 appropriate instrument, as in the method 

 of F. E. Ives, which was explained. This 

 solution of the problem gives very beautiful 

 results, but the necessity for an auxiliary 

 instrument interferes with its general avail- 

 ability. It does not seem probable there- 

 fore that photography in colors will soon 

 interfere seriously with that photography 

 in light and shade with which most of us 

 have had to content ourselves thus far. 



Investigations in the infrf^-red region of 

 the spectrum were notv considered, the fore- 

 most place being given to Langley's recent 

 work, which will undoubtedly make it possi- 

 ble to determine in large measure to what 

 extent the cold bands in the heat spectrum 

 are due to atmospheric absorption, and 

 which of them are produced by absorption 

 outside of the earth's atmosphere. Notice 

 was given to the work of Snow, Rubens, Ang- 

 strom, Paschen and Percival Lewis in their 

 studies of the infra-red spectra of various 

 chemical elements. 



In regard to the visible spectrum, re- 

 ference was made to Rowland's extensive 

 work in the determination of wave-lengths 

 for all the chemical elements; to the recent 

 discovery of argon and helium; to the 

 grouping of spectral lines by Kayser and 



Runge; to Keeler's spectroscoi:)ic study of 

 Saturn's rings, and Hale's use of the spec- 

 troheliograph . 



In the domain of polarized light the work 

 of Nichols and Snow, of Merritt, of Mars- 

 ton and of Crehore was duly noticed, in- 

 cluding the application to gunnery. 



Physiological optics is a subject too large 

 to receive its proper share of attention in 

 an address chiefly on physical optics. Mrs. 

 Franklin's theory of light sensation was 

 discussed, and a brief account was given of 

 Mayer's ingenious experiments on simul- 

 taneous color contrast, which have been con- 

 firmed by the experiments of the author. 

 Reference was then made to Ferry's law of 

 retinal persistence, and its application to 

 the explanation of the ' artificial spectrum 

 top,' which has excited such general inter- 

 est during the last year. That it should 

 have been copyrighted is deemed a prece- 

 dent that may yet result in an attempt to 

 copyright the solar spectrum. 



In addition to the address of the Vice- 

 Preisdent twenty-five papers were read in 

 full and three by title, about the same number 

 as last year at Brooklyn. 



1. Expansion of Jessop^s Steel, Measured by 

 Interferential Method (30 'm.), by E. W. 

 MoELEY and Wm. A. Rogers. The Fizean ■ 

 method with numerous adaptations and 

 improvements was employed to determine 

 the thermal expansion of Jessop steel, with 

 the result that the measurement of the elon- 

 gation is now much more accurate than the 

 temperature observations. The latter ap- 

 pears to be correct to ±0.1° C. and hence the 

 coefficient of expansion is correct to 0.1%; 

 which is about the accuracy at present at- 

 tained by other methods. The authors 

 expect to improve the thermometric part of 

 the apparatus and attain an accuracj^ much 

 greater than at present. 



2. Flow of Alternating Currents in an Electric 

 Cable (20 m.), by M. I. Pupin. This 



