182 



SCIENCE. 



[N. S. Vol. XVI. No. 396. 



AbsorptioH Spectrum of Carbon: E. L. 

 Nichols and E. Blaker, Cornell Uni- 

 versity. Presented by Dr. Blaker. 

 The selective radiation of carbon has 

 already been shown. A further series of 

 experiments have been made during the 

 past year on the selective absorption of 

 carbon. Deposits have been obtained by 

 deposition on glass in vacuum tubes be- 

 tween terminals of carbon, in series with 

 the secondary of an induction coil, the 

 residual gas being acetylene. These de- 

 posits vary in composition without doubt, 

 and show different absorption for different 

 conditions of deposition, depending on the 

 pressure of the residual gas. 



Deposits made on platinum by ' flashing, ' 

 as in the ordinary incandescent lamp, and 

 then transferred to glass and studied with 

 the spectrophotometer, show the same pecul- 

 iarities as have been shown to be obtained 

 using gio-wang treated carbon. The dis- 

 persion has not been fully studied yet. 



The paper will be published in the Pliys- 

 ical Revieiv. 



Persistence of Vision in Color-Mind Sub- 

 jects: Frank Allen, Cornell University. 

 In this investigation, color-blind subjects 

 were studied by the Nichols method of the 

 measurement of the persistence of visual 

 impressions. A sectored disc was rotated in 

 front of the slit of a spectrometer at such a 

 speed that the flickering of the part of the 

 spectrum under observation just became 

 imperceptible. The speed at this instant 

 was electrically recorded on a piece of 

 paper carried on a chronograph cylinder. 



The measurements when plotted as ordi- 

 nates with wave-lengths as abscissas form a 

 'persistency curve' which is parabolic in 

 shape, convex toward the axis of abscissas, 

 and mth the apex at the D line. Under 

 the same conditions of brightness of the 

 spectrum and adaptation of the retina the 

 persistency curve is invariable for the same 



subject and even for persons of about the 

 same age, providing their color vision is 

 normal. Color-blind persons obtain per- 

 sistency curves which usually coincide with 

 normal curves in part, but which always 

 have one or two elevations. The positions 

 of these characteristic elevations afford a 

 means of classification ; for they occur only 

 in the parts of the curve corresponding to 

 the red, green and violet of the spectrum. 



The Young-Helmholtz theory postulates 

 three fundamental color sensations— red, 

 green and violet. In color-blind subjects 

 it may be expected that any one of these 

 may be absent or modified alone, or that 

 any two may be absent or modified, or that 

 all three may be absent. The last phe- 

 nomenon is that of total color-blindness, 

 and its existence is not provided for by the 

 Yoimg-Helmholtz theory, apart from total 

 blindness. There are thus seven possible 

 types of color-blindness, and in this investi- 

 gation persistency curves corresponding to 

 six of them have been obtained, the miss- 

 ing one being that in which an elevation is 

 to be expected in the violet end of the 

 curve. One case of total color-blindness is 

 also described which is remarkable in that 

 the brightest part of the spectrum is in its 

 normal position to him. No similar case 

 has yet been described. 



In this research twenty-six cases of color- 

 blindness were examined, and their results 

 permit a very complete and systematic 

 classification, such as is obtained by no 

 other method. The conclusion reached is 

 that the fundamental sensations are red, 

 green, violet and white. The assumption 

 of more than these three color-sensations is 

 strongly opposed by these experiments. 



Heat of Vaporisation of Liquid Air: J. S. 



Shearer, Cornell University. 



This paper will appear in the Physical 

 Review. 



