588 



SCIENCE, 



[N. S. Vol.. XIV. No. 355. 



2. There are forces exactly opposite to 

 those of the perfect fluid. 



3. These new forces are most probably 

 due to the viscosity of the medium. 



4. The new forces in conjunction with the 

 forces of a perfect fluid make possible a 

 complete and clear explanation of the 

 laminae and flutings produced in a sound 

 wave. (To be printed in the Phil. Mag. ) 



6. ' Interferometer Curves ' : J. C. Shedd, 

 Colorado College. 



The general equation of the interference 

 curves is found to be a conic and the con- 

 ditions for obtaining the various forms are 

 determined by considering the question of 

 eccentricity. 



The various cases are taken up in detail 

 and the experimental manipulations neces- 

 sary for obtaining them are explained. 



7. ' On the Absorption Spectrum of Iodine 

 in Solution ' : Edward L. Nichols and 

 William W. Coblentz. 



That iodine dissolved in carbon disul- 

 phide, although opaque to the visible spec- 

 trum, transmits the infra-red rays freely, 

 has long been known, but no systematic 

 studies of the spectrum of such solutions 

 appfear to have been made. In the study 

 of the visible spectrum a horizontal slit 

 spectrophotometer was used. Quantities 

 of iodine varying from 3.3 mg. to 0.017 

 mg. per cubic centimeter were dissolved 

 and their absorption spectra measured. A 

 single broad band was found, having its 

 maximum at A = .52/^, the transmission 

 curve being steeper on the side towards the 

 violet. For the solution containing 0.017 

 mg. per cc. the transmission in the center 

 of the band was 80 per cent. With in- 

 creasing concentration the band widens 

 and becomes more dense. Solutions con- 

 taining more than .25 mg. per cc. are opaque 

 in the center of the band, and the region of 

 opacity extends as the amount of iodine in 

 solution is increased until the entire visible 

 spectrum is obscured. Observations upon 



iodine dissolved in alcohol showed a very 

 different absorption spectrum. Such solu- 

 tions were opaque in the violet, the trans- 

 mission increasing steadily towards the red. 

 The form of the curves was such as to in- 

 dicate an absorption band of which one 

 side only lies in the visible spectrum, the 

 center being in the ultra-violet. To extend 

 these measurements to the infra-red spec- 

 trum a Nichols radiometer was employed. 

 Readings of the transmission of various 

 solutions were made out to 2.7,^-, beyond 

 which wave-length the solvent itself rapidly 

 becomes opaque. It was found that all so- 

 lutions rose rapidly in transmitting power 

 with increasing wave-length and became 

 completely transparent between 1.0,^ and 

 l.l/-i, between which region and 2.7/^, iodine 

 appears to exert no absorbing power what- 

 ever. 



7a. ' A Preliminary Communication on 

 the Pressure of Light and Heat Eadiation ' : 

 E. F. Nichols and G. F. Hull. 



The experiment consisted of two parts: 

 (1) The determination of the light pressure 

 by observing the deflection, either static or 

 ballistic, of a torsion balance when one 

 vane of the balance was exposed to light, 

 and (2) the determination, in ergs per sec- 

 ond, of the intensity of the light falling 

 upon the vanes. The image of an aperture, 

 upon which the rays from an arc lamp were 

 concentrated by two condensing lenses, was 

 focused in the plane of the glass vanes 

 placed symmetrically with regard to a rota- 

 tion axis held by a quartz fiber of known 

 torsion coefficient. The torsion balance was 

 covered by a bell jar connected to pressure 

 gauges and a mercury pump. To eliminate 

 the disturbing action due to the residual gas 

 in the receiver, the following devices were 

 used: (1) The vanes were silvered and 

 highly polished, thus making the absorp- 

 tion small and the reflection percentage 

 large. (2) The silver surface of one vane 

 was turned towards, and of the other, from, 



