THE PHOTOGRAPHY OF COLORS. 547 



ferent simple or complex colors. This is what is called isochro- 

 matism. 



By the aid of these improvements M. Lippmann has succeeded 

 in fixing on his plates images of marvelous beauty. The colors 

 have an inconceivable brightness and delicacy of shading. They 

 have nothing in common with painted copies of photographs, 

 which simply enhance the photographic images with coloring. 

 The photographic proofs obtained by M. Lippmann have a 

 strength of coloring and a richness of tone which no water-color 

 picture has ever attained. This is because, in his photography, 

 the registration of the color is combined with the accumulation 

 of all the colored rays. 



It is not necessary to say that the learned professor in the Sor- 

 bonne has not sought to draw an industrial profit from his inven- 

 tion. It is free to all who may hereafter wish to direct their in- 

 vestigations that way. There remains much still to be done be- 

 fore all the improvements can be given to science. The problem 

 now is to advance from the fixation of the colors on the sensitive 

 plates to their reproduction on paper. Theory permits the pre- 

 diction that regular reflection by a metallic mirror may be replaced 

 before long by the diffusion of light over a dead surface. It is, 

 then, permissible to hope, without contradiction of the theory of 

 interferences, that the multiplication of proofs by simple printing 

 on paper is only a matter of time. It is easy to understand how 

 much the arts and science are interested in the progress of the 

 photography of colors. 



While the pigmentary colors used by painters are made of 

 substances which light may change in the long run, interference 

 colors, which are produced by the vibratory movement alone, de- 

 pend solely on the physical and mechanical conditions of the ex- 

 periment, and are not subject to alteration by time. Photogra- 

 phy of colors will permit the faithful reproduction of the pictures 

 of the masters, and will also assure the reproduction of meteor- 

 ological phenomena which may be of considerable importance in 

 future studies of astronomical science. Translated for The Popu- 

 lar Science Monthly from the Revue des Deux Mondes. 



A PRACTICAL course of instruction in psycho-physiology was given in Univer- 

 sity College, London, during the Easter term, by Dr. L. E. Hill. The plan of the 

 course was to take the student methodically over the several senses, and familiarize 

 him with the methods by which the new branch of science known as physiological 

 psychology or psycho- physics determines the precise manner in which sensation 

 varies, both quantitatively and qualitatively, with variations of the stimulus, of 

 the particular portion of the sensitive surface stimulated, etc. The Athenaeum 

 acknowledges the backwardness of England as compared with the United States 

 and Germany in the systematic laboratory instruction of students in this subject. 



