SKETCH OF PROFESSOR HELMHOLTZ. 233 



honor of an engagement as contributor to the " Berlin Encyclopaedic 

 Lexicon of Medical Sciences." The most important among the numer- 

 ous articles which he wrote during this period is one on the chemical 

 analysis of the consumption of matter by muscular action ; another on 

 animal heat, especially in relation to the question whether the body 

 of an animal throws out the same amount of heat which is produced 

 by the combustion and transformation of its food ; and a third, which 

 treats of the development of heat through muscular action. 



The great variety of subjects treated in his short publications 

 during these years excludes the hypothesis that there was in his stud- 

 ies a gradual growth toward the discoveries which uphold his world- 

 wide fame, and for which every branch of study related to the j^hysi- 

 cal sciences is so greatly indebted to him. There are, however, im- 

 pressions which every reader of these papers receives. Helmholtz is 

 nobody's pupil ; he stands on the basis of personal observation, and 

 speaks whatever he believes to be true. To show how independently 

 his mind was developed, it may be stated that he could not be in- 

 duced to attend a single lecture on physical science while a student 

 in Berlin. 



In 1847, being consequently only twenty-six years of age, he pub- 

 lished his important work, "The Conservation of Force." The dis- 

 covery of this principle of Nature has been of the greatest moment to 

 the progress of the whole range of physical sciences. This law is, in 

 fact, indispensable to a sound understanding of any and every phe- 

 nomenon in the animate and inanimate world. And Helmholtz opened 

 his scientific career with a production that would have worthily closed 

 a long life of study and fame. 



After the publication of " The Conservation of Force," he was ap- 

 pointed prosector at the Anatomical Institute in Berlin, where he re- 

 mained about a year. In 1849 he was called to the chair of Physiol- 

 ogy at the University of Konigsberg. He accepted it, and filled it for 

 a period of nearly six years, in which he made some brilliant discov- 

 eries and inventions, which have ]3roved a blessing to thousands of 

 sufferers. 



It had been generally held that the time needed for conceiving a 

 thought, and experiencing sensations, could not be measured. Prof. 

 Helmholtz (1850-'ol) invented, however, a series of highly-ingenious 

 processes for measuring the duration of any action, however swift, 

 and demonstrated, in a number of papers, that there is a lapse of time 

 before a sensation caused on one end of a nerve is felt at the other. 

 He proved, for example, that, when we touch a thing, it takes a little 

 time before we know that we touched it, and that, however rapid and 

 seemingly instantaneous our actions be, some small period of time 

 must elapse before we can begin to execute the mandates of our will. 

 In 1851 he invented a mirror with which to examine the retina of 

 the eye in living beings, and in the following year he described an 



