INTRODUCTORY NOTE 



HERMANN LUDWIG FERDINAND VON HELMHOLTZ was born at 

 Potsdam, near Berlin, on August 31, 1821. His father was a 

 man of high culture, a teacher in the gymnasium, whose in- 

 fluence ensured to his son the foundations of a broad general 

 education. His mother was a descendant from William Penn, 

 the English Quaker. 



Helmholts early showed mathematical ability, and wished 

 to devote his life to the study of physics; but practical 

 considerations led him to take up medicine, and he became 

 a surgeon in the Prussian army. He began the publication of 

 original contributions to science in 1842, and for fifty-two 

 years, till his death in 1894, he continued to produce in an 

 unbroken stream. He held a succession of academic positions, 

 teaching physiology at Konigsberg, Bonn, and Heidelberg, and 

 for the last twenty-three years of his life filling the chair of 

 physics at Berlin. 



The titles of his professorships, however, give a very inad- 

 equate idea of his range. His contributions to science cover 

 medicine, physiology, optics, acoustics, mathematics, mechanics, 

 and electricity. His interests in science and art came together 

 in his work on esthetics, and he had a lively appreciation of 

 painting, poetry, and music. 



The practice of popular lecturing on scientific subjects was 

 almost unknown in Germany when Helmholts began, and he did 

 much to give it dignity and to set a standard. His own lectures, 

 as the reader of the following papers will perceive, are master- 

 pieces of their kind. "The matter," says a biographer, "is dis- 

 cussed by a master, who brings to bear upon it all his wealth 

 of learning and research, while there is the ever-enduring in- 

 terest that attaches to an exposition by one who is giving forth 

 from his own treasury." It is fortunate for the layman when 

 a scientist and thinker of the first order has the skill and the 

 inclination to share with the outside world the rich harvest of 

 his brilliant and laborious research. 



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