BARON VON HELMHOLTZ. 593 



i^ervatioii of Force," gave him at once au acknowledged rank 2^s facile 

 princeps among the chief investigators in natural science. This was 

 accompanied by other notable contributions ; especially those on 

 "The Nature of Putrefaction and of Fermentation," published in 

 1843 ; " On Animal Heat " ; and on " The Consumption of Tissue dur- 

 ing Muscular Action," in which was considered the question whether 

 the living body gives off as much heat as is produced by the combus- 

 tion and change of the food it takes in. 



In 1849, Helmholtz became Professor of Physiology in the Univer- 

 sity of Konigsberg, where he made notable investigations on " The 

 Rapidity of Propagation of Nerve Excitation." By ingenious methods, 

 of his own devising, for measuring extremely small differences of 

 time, he was enabled to demonstrate that thought is not instantaneous, 

 that it takes a definite period for us to become conscious of a fact, and 

 that a certain measurable time elapses between the willing of a move- 

 ment and the executing of it. 



Helmholtz's original and intricate researches begun thus early and 

 including every department of physiology and of physics, are a record 

 of amazing originality, acuteness, and industry, largely in new fields. 

 They are especially remarkable for accuracy of observation, and quick 

 discernment in the interpretation of the phenomena investigated. 

 Nothing seemed so insignificant as to escape his notice, and little was 

 so obscure as to defy his explanation. 



Among the fruitful practical results of Helmholtz's untiring activi- 

 ties, we do not exaggerate in placing a superlative value upon his 

 invention of the Opthalmoscope, — not only a most precious endowment 

 of science, but as bestowing immeasurable benefits upon the whole 

 human race. 



We may well say, with Hasner : *' The ophthalmoscope is not only 

 the most valuable boon to ophthalmology, but is also one of the great- 

 est creations of our century. What the telescope is to astronomy, 

 the ophthalmoscope is to ophthalmology. The telescope owed its 

 existence to an accident, but the ophthalmoscope is absolutely the 

 mature offspring of theory, and is therefore a greater ornament than 

 the former, not only to Helmholtz, its originator, but also to the age 

 itself, which has not been here indebted to blind chance for great dis- 

 coveries, but has known how to deduce them from exact and laborious 

 scientific investigations." 



Zehender, himself illustrious as an author and teacher, says of 

 Helmholtz : " For more than two hundred years physiologists and 

 mathematicians earnestly and with great sagacity sought for a solution 



VOL. XXX. (n. S. XXII.) 38 



