46 HERMANN VON HELMHOLTZ 



their distribution in space, but are unalterable in their pro- 

 perties) was admitted by all physicists to obtain in every 

 change of organic and inorganic nature. The great prin- 

 ciple of the conservation of energy, which Helmholtz placed 

 beside this law, postulates that all forces are to be measured 

 in terms of mechanical force, and that all forms of energy are 

 ultimately kinetic, so that the final aim of natural science 

 must be to reduce itself to mechanics. 



Equipped only with such literary matter as the library of 

 the Gymnasium could afford him during his residence in 

 Potsdam, unaware of Robert Mayer's nine-page note 'On 

 the Forces of Inorganic Nature', published in Wohler and 

 Liebig's Annalen der Chemie in 1842, after it also had been 

 rejected by Poggendorff, and of the same author's treatise pub- 

 lished in 1845, on 'Organic Motion in relation to Metabolism', 

 Helmholtz had by 1843-4 completed the essentials of the 

 work which Kirchhoff estimated twenty years later as the 

 most important contribution to natural science made in our 

 era, while Hertz, Helmholtz's great pupil, says of it that 

 ' Physical research had been diverted by the close of the 

 century into an entirely new channel. Under the over- 

 mastering influence of Helmholtz's discovery of the conser- 

 vation of energy, its object was henceforward to refer all 

 phenomena in last resort to the laws which govern the 

 transformation of energy '. 



But while the great significance of Helmholtz's work was 

 immediately recognized by the younger generation of scientific 

 men, the older physicists still held aloof from it, on the ground 

 that it was a relapse into the 'nature-philosophy' of Hegel. 

 In other quarters, again, where the importance of the great 

 law was admitted, the honour of its discovery was withheld 

 from Helmholtz. It was said that he had borrowed the idea 

 from Dr. Julius Robert Mayer, a Heilbronn physician, who 

 had published a thesis on the same subject, and had even 

 determined the mechanical equivalent of heat. ' This report,' 

 says du Bois-Reymond, ' has lasted, like the fame of Helmholtz's 

 treatise, to the present day, and has been greedily accepted 

 by those who love to trail shadows across the sunlight.' 



As regards priority, Helmholtz, after he had become 

 acquainted with the writings of Robert Mayer, took every 



