xix 



dent that in 1843 the young doctor was on the track which Pastenr 

 has since followed with snch marvellous success. 



But though the first work of Helmholtz was to prove that the 

 intervention of life was essential to produce certain results which had 

 been wrongly ascribed to direct chemical action, he was soon occupied 

 with a group of converse propositions which show that the action of 

 life itself is subject to the laws of mechanics, physics, and chemistry. 

 The celebrated essay on the " Conservation of Force," or as we 

 should now call it the " conservation of energy," was published in 

 1847. Helmholtz was led to the discussion of this subject by reflec- 

 tions of the nature of " vital force." He had convinced himself that 

 if it were true that living organisms could restrain or liberate the 

 action of chemical and physical forces, perpetual motion would be 

 realised. This compelled him to ask what relations must exist 

 between the various kinds of natural forces for perpetual motion to 

 be possible, and then to enquire if these relations actually exist. 



The argument, though addressed to physicists, was intended for 

 the benefit of physiologists. The first part is devoted to a proof 

 that if all natural forces are " central," i.e., act towards fixed centres, 

 and depend solely on the distances and masses of the mutually 

 reacting bodies, the law of the conservation of energy must hold 

 good. The latter part of the paper is a masterly discussion of the 

 application of the law to the different branches of experimental 

 science. It is unnecessary to trace these applications in detail, or to 

 define precisely with respect to each of them the relative positions of 

 Helmholtz and of his most distinguished contemporaries. The essay 

 is worthy of such minute discussion, but its value is to be judged 

 chiefly by the effect it produced. Though von Helmholtz was not 

 an originator of the doctrine of the conservation of energy ; though 

 when his essay was written he knew little of Joule, and nothing of 

 Mayer, he viewed the whole question from a standpoint far in 

 advance of the majority of the scientific men of that day. His 

 paper was refused admission to ' Poggendorff's Annalen,' and he has 

 told us that Karl Jacobi was his only supporter among the older 

 members of the Physical Society of Berlin. The result of a sharp 

 struggle was entirely in favour of the young doctor. William 

 Thomson, in England, and Helmholtz, in Germany, within a few 

 weeks, compelled their respective countrymen to listen to, and before 

 long to accept, the doctrine that energy, like matter, can neither 

 be created nor destroyed, that though protean in form, it is unchange- 

 able in quantity. The last application of this principle was cha- 

 racteristic of the author. The problem of "vital force" led him 

 to the doctrine of the conservation of energy ; the last of the ques- 

 tions which he discussed in the light of that doctrine was the con- 

 servation of energy in animals and plants^ 



d 2 



