NEW APPLICATIONS OF LIGHT. 



feet that books and periodicals are illustrated with an 

 amount of accuracy and beauty that would have been 

 impossible, even twenty years ago, except at a prohib- 

 itive cost. 



It has long been the dream of photographers to dis- 

 cover some mode of obtaining pictures which shall repro- 

 duce all the colors of nature without the intervention of 

 the artist's manipulation. This was seen to be exceed- 

 ingly difficult, if not impossible, because the chemical 

 action of colored light has no power to produce pigments 

 of the same color as the light itself, without which a 

 photograph in natural colors would seem to be impos- 

 sible. Nevertheless, the problem has been solved, but 

 in a totally different manner; that is, by the principle of 

 " interference," instead of by that of chemical action. 

 This principle was discovered by Newton, and is exem- 

 plified in the colors of the soap bubble, and in those of 

 mother-of-pearl and other iridescent objects. It de- 

 pends on the fact that the differently colored rays are of 

 different wave-lengths, and the waves reflected from two 

 surfaces half a wave-length apart neutralize each other 

 and leave the remainder of the light colored. If, there- 

 fore, each differently colored ray of light can be made to 

 produce a corresponding minute wave-structure in a 

 photographic film, then each part of the film will reflect 

 only light of that particular wave-length, and therefore 

 of that particular color, that produced it. This has actu- 

 ally been done by Professor Lippmann, of Paris, who 

 published his method in 1891; and in a lecture before 

 the Royal Society in April, 1896, he fully described it 

 and exhibited many beautiful specimens. 1 



'This lecture is reported in Nature, vol. liii. p. 617. 



