iv PREFACE 



The professional career of Helmholtz was unparalleled 

 in the history of professions. He was Military Surgeon 

 in the Prussian army five years ; Teacher of Anatomy 

 in the Academy of Arts in Berlin one year ; Professor 

 of Pathology and Physiology in Konigsberg six years ; 

 Professor of Anatomy in Bonn three years ; Professor 

 of Physiology in Heidelberg thirteen years ; Professor 

 of Physics in the University of Berlin about twenty 

 years, till he became Director of the new * Physikalisch- 

 Technische Reichsanstalt '. He occupied this post during 

 the last years of his life, still continuing to give lectures 

 as Professor of Physics. 



Beginning with the generous aid and co-operation of 

 Werner von Siemens, and ultimately supported by the 

 financial resources of their country, Helmholtz created 

 the Reichsanstalt, which has already conferred inestim- 

 able benefits, not only on Germany, but on the whole 

 world. It is an example, tardily and imperfectly fol- 

 lowed by Great Britain and other countries only now 

 beginning to learn that scientific research yields results 

 which are valuable, not merely for the discovery of 

 truths appreciated only by scientific workers, but for 

 contributing in many ways to the welfare of the whole 

 people. 



The Faraday Lecture, delivered by Helmholtz before 

 the Fellows of the Chemical Society in the theatre 

 of the Royal Institution on Tuesday, April 5, 1881, 

 was an epoch-making monument of the progress of 

 Natural Philosophy in the nineteenth century, in 

 virtue of the declaration, then first made, that elec- 

 tricity consists of atoms. Before that time atomic 



