May 26, 1899.] 



SCIENCE. 



737 



direct vision. It is probable, therefore, 

 from the similarity of the results at the two 

 angles, that it continues to do so in the 

 more peripheral parts of the retina, al- 

 though it has lost its other function, of 



• color- sensation. 



The results at 70° confirm in a general 

 way the measurements of von Kries. His 

 results are given in Table III., with the 

 column for 70° from the flicker experi- 

 ments, both also reduced to the value unity 



an the yellow for purposes of comparison. 



Table III. 



VON Keies. Whitman-. 



Original Original 



Values. Reduced. Values. Reduced. 



E. 1.35 .199 .079 .130 



•0. 4.03 .594 .222 .337 



Y. 6.78 1.000 : .660 1.000 



Y.G .478 .724 



•G. 4.92 .726 .391 .592 



E.G. 3.87 .571 



G.B .344 .521 



B. .193 .292 



V. .86 .127 



The two sets of measurements, though 

 differing considerably in detail, show a pro- 

 gression in brightness of a similar charac- 

 ter, especially as to the position of the max- 

 imum. An inspection of the table makes 

 it evident that differences in the results 

 might possibly be explained by the assump- 

 tion of slight differences in the pigments 

 used by the two observers ; but it is per- 

 haps more probable that the difference is a 

 real one, caused by the fact that my obser- 

 vations were made in a darkened room, 

 and, therefore, with an eye more 'adapted 

 for darkness ' than that of von Kries, who 

 worked in a well-lighted place. 



While it appears evident, as von Kries 

 holds, that the color-perceiving apparatus 

 is of importance in determining the bright- 

 ness of any color periphei-ally seen, it is 

 plain that — in the language of his theorj^ — 

 the apparatus for twilight vision plays a 

 /more important part than in the central 



portions of the retina. For the diminution 

 of the reds and increase of the blues in 

 brightness are characteristic only of faint 

 illumination by direct vision — illumination 

 fainter than the lowest at which the flicker 

 method can be advantageously used (Phys- 

 ical Reviexo, loc. cit., p. 247), whereas they 

 are shown by these experiments to exist in 

 the outer regions of the retina under con- 

 ditions of considerable brightness. 



It may be said, in conclusion, that the 

 brightness-sensation of the retinal per- 

 ipherj', so far as it differs from that of the 

 central portions, differs from it in the same 

 direction, though not so greatly, as in the 

 other two types of complete color-blind- 

 ness. 



Frank P. Whitman. 



Adelbekt College. 



AN EXTENSION OF HELIIROLTZ'S THEORY 

 OF THE HEAT OF THE SUN."^ 



On the occasion of the Kant Commemo- 

 ration at Konigsberg, February 7, 1854, 

 Helmholtz delivered an address on the ' In- 

 teraction of Natural Forces,' in which he laid 

 the foundation of the modern theory of the 

 sun's heat. The whole address, with the 

 principal formuhe bj' which the numerical 

 results were obtained, was translated into 

 English and published in the Philosophical 

 Magazine for 1S56. In this paper the author 

 discusses the conservation of energy, which 

 ■ he had been so instrumental in establishing 

 upon a sound mathematical basis ; and as- 

 cribes the maintenance of the sun's heat to 

 the potential energy given up by the par- 

 ticles in descending towards the center of 

 his globe. On the hypothesis that the solar 

 sphere is of homogeneous density he sub- 

 jects the j)roblem to computation, and finds 

 that the heat developed by a very small 

 shrinkage of the mass will be sufficient to 



* Read before the Philosopbioal Society of Wash- 

 ington, May 13, 1899. 



