106 SCIENTIFIC THOUGHT. 



By his work on organic chemistry, by his many con- 

 troversies, such as that on fermentation, by his popular 

 letters on chemistry, and especially by his great intlu- 

 ence as a teacher, Liebig himself did much to bring 

 about an alliance of the separate sciences and a connec- 

 tion between practical pursuits and abstract research, and 

 to draw attention to the interdependence of the various 

 10. forces of nature. Only second in influence was Johannes 



JohnMuller. _ '' 



Mliller of Berlin. Among the many expressions which 

 took their origin in the circle of studies suggested 

 by these influences, we may select three as giving 

 increasingly clear emphasis to the point now under 

 consideration — viz., the correlation of all the physical 

 forces of nature. These expressions are those of the 

 convertibility of forces, of the existence of a common 

 measure of force, and of the conservation implying 

 the perdurability of a certain quantity — now termed 

 Energy — of which all phenomena are merely a partial 

 exhibition. They are connected with the names of 

 Karl Friedrich Mohr, Julius Eobert Mayer, and Her- 

 mann Helmholtz. 



Were it my object merely to write the history of 

 science, I should probably follow the example of some 

 historians ^ and omit altogether the first of these names 

 in the present connection. But as my object is to write 

 the history of scientific thought, I feel bound to give a 



^ Mach, iu his recent very lucid 

 and valuable work, ' Die Priiici- 

 pien der Wiirmelehre,' Leipzig, 

 1896, does not mention Mohr. On 

 the other side, Helm (' Die Ener- 

 getik,' 1898, p. 9) mentions Mohr 

 and likewise Planck ('Das Priucip 

 der Erhaltung der Energie,' 1887, 



p. 21). Tait's first edition of 

 'Recent Advances,' 1874, does not 

 contain Mohr's name. The third 

 edition gives a full account of 

 Mohr's early papers (pp. .51 and 

 60, &c.) See also the appreciative 

 article on K. F. Mohr in the ' Ency. 

 Brit.' 



