THE SCIENTIFIC SPIRIT IN GERMANY. 



199 



which declares that the differences of the sensations of 

 light and colour, of sound, of touch, &c., do not depend 

 upon the mode of irritation, nor even upon the different 

 structure of the specific nerves, but upon the nature of 

 the central sense organ. In the school of Miiller the 

 phenomena of voltaic electricity, which had been so seduc- 

 tive and misleading to an earlier school of physiologists 

 not experienced in the methods of exact research, were 

 again -subjected to scientific investigation, and led to 

 the brilliant researches with which the name of Du Bois- 

 Eeymond is so intimately connected. He is as ready as 

 Helmholtz, who in his two great works on physiological 

 optics and musical acoustics has founded new branches 

 of science, 1 to acknowledge the leadership of Johannes 



1 Helmholtz (1821-95), equally 

 celebrated as physiologist and ma- 

 thematical philosopher, was edu- 

 cated under the influence of Jo- 

 hannes Miiller on the one side, of 

 Jacobi and the Konigsberg school 

 of mathematicians (Bessel and Neu- 

 mann) on the other. If we add to 

 this that he also made a profound 

 study of those far-reaching specula- 

 tions which originated in the phil- 

 osophy of Kant, we realise how rare 

 is the combination of ability and 

 knowledge which he has brought to 

 bear on the discussion of the most 

 advanced problems in physics, 

 biology, and psychology. In the 

 sequel I shall have to refer so 

 frequently to his writings that I 

 confine myself here to giving the 

 date of his principal, his epoch-mak- 

 ing publications : 1847. 'Ueberdie 

 Erhaltungder Kraft'; 1858. 'Ueber 

 die Integrate der hydrodynamischen 

 Gleichungen, welche der Wirbel- 

 bewegung entsprechen ' both re- 

 printed in ' Wissenschaftliche Ab- 

 handlungen,' Leipzig, 1882 and 



1883, 2 vols. These two Memoirs 

 may be considered as corner-stones 

 of two of the most important mo- 

 dern theories in physical science, 

 the "conservation of energy" and 

 the " theory of vortex motion." In 

 both, the name of Helmholtz is in- 

 timately allied with that of William 

 Thomson (Lord Kelvin). Equally 

 important and more comprehensive 

 have been his researches in the 

 physiology and psychology of sense- 

 perceptions in his ' Physiologische 

 Optik,' Leipzig, 1867; 'Lehre von 

 den Tonempfindungen,' Braunsch- 

 weig, 1863. 



Helmholtz has also contributed 

 largely to the discussion of two very 

 important branches of modern spe- 

 culation first, the theoretical views 

 on the nature of electrical pheno- 

 mena expressed by the opposite 

 conceptions of Wilhelm Weber in 

 Germany and Faraday in England ; 

 second, the origin of geometrical 

 axioms, especially the axiom refer- 

 ring to parallel lines. A great 

 interest in this subject had been 



