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THE POPULAR SCIENCE MONTHLY. 



ophtlialmometer, or an instrument for measuring the eye, which has 

 proved of much service. His next researches were on the field of spec- 

 tro-analysis, and he demonstrated that the results obtained by painters 

 in mixing colors do not correspond with those of mingling the pure 

 spectral colors of solar light or of other lights decomposed with a 

 prism. He showed, for example, that, when yellow and blue rays of 

 light are combined, the color produced is white, and not green. In 

 connection with this subject, he entered into an admirable analysis of 

 the extent and limits of human observation, and totally refuted at the 

 same time Sir David Brewster's alleged decomposition of solar light. 



In 1855 Helmholtz was called to the University of Bonn as Pro- 

 fessor of Anatomy and Physiology, and director of the Anatomical 

 and Physiological Institute. Three years later he removed to the 

 University of Heidelberg, to fill a chair of Physiology, which he con- 

 tinued to occupy for more than twelve years. It would be tedious to 

 enumerate every thing that his patient labor and the unerring logic 

 of his mind demolished, while there, in the snug but shaky edifices of 

 conservative science. He scattered the results of his researches with 

 a liberal hand all over Germany. Every scientific periodical was 

 honored by him with a contribution on its own specialty. There is, 

 however, one class of his articles that appeared during this period 

 which must not be overlooked. He had rendered valuable services 

 toward an exact understanding of the mechanism of the eye, and had 

 observed the physical laws of vision. He now turned his attention to 

 a subject of equal importance. He investigated the mechanism of the 

 ear, and searched for the laws of sound. His discoveries are laid down 

 in his " Doctrine of the Sensations of Sound, as a Physiological Basis 

 for the Theory of Music." It contains a complete analysis of the 

 conditions of harmony, and reduces its sesthetic principles to a few 

 fundamental physical laws. 



Helmholtz's new doctrines of sight and sound have been univer- 

 sally received, and his fame will last as long as they continue to be 

 among the main pillars of physical science. His name is also insep- 

 arably connected with the doctrine of the conservation of force, which 

 subsequent investigation at the hands of others has shown to be the 

 key-note of every law of Nature. Its bearing on the doctrine of evo- 

 lution is, however, so strong and favorable that, like that doctrine, it 

 will need much time before it receives an unreserved acceptance. 

 Helmholtz tested, a few years ago, the progress which the doctrine of 

 evolution has made, by asking the congress of natural philosoj^hers, 

 assembled at Speier, to declare, openly, who of them were in favor of, 

 and who against, Darwinism. The roll was called, and there was not 

 one against it. Helmholtz removed, in 1871, to Berlin, and holds there 

 a professorship in the University. 



