184 



SCIENTIFIC THOUGHT. 



aware of the importance of mathematical presentation of 

 their doctrine, and the two former have in fact done 

 more than any one else to introduce mathematics into 

 chemistry. But they maintain that their exact treatment 

 is not arrived at by introducing hypothetical quantities 

 such as the atomic and other theories are founded upon, 

 but by contenting themselves with measuring such quan- 

 tities as are presented directly in observation, such as 

 energy, mass, pressure, volume, temperature, heat, elec- 

 tric potential, &c., without reducing them to imaginary 

 mechanical or kinetic quantities.^ To what extent they 



A great many aspects of physical 

 science which have been more 

 prominently brought forward by 

 the modern school of " Ener- 

 getics " are to be found discussed 

 in Mach's much earlier writings. 

 To his valuable 'Principien der 

 Wiirmelehre ' (Leipzig, 1896) I have 

 frequently had occasion to refer in 

 this chapter. 



^ In recent discussions and 

 treatises two distinct tendencies 

 must be distinguished. First we 

 have tlie very useful effort to bring 

 about a correlation of the differ- 

 ent departments of physics and 

 chemistry, including their applica- 

 tions in industry and in physi- 

 olog)', by the introduction of the 

 conception of energy and the 

 principles of its conservation and 

 transformation. This dates prac- 

 tically from the publication of 

 Thomson and Tait's ' Natural 

 Philosophy. ' The theoretical 



foundations of this undertaking 

 have been very fully discussed, 

 notably in Germany. I mention 

 only the valuable series of writ- 

 ings of Prof. Max Planck, a list 

 of which is contained at the end 

 of his ' Thermodynamik ' (Leipzig, 

 1897). They begin with his prize 

 essay (' Das Princip der Erhaltung 



der Energie,' 1887) and his earlier 

 dissertation (Munich, 1879) " On 

 the Second Law." Out of this an- 

 other endeavour has grown. The 

 aim is to make the conception 

 of energy the fundamental notion, 

 and by following its physical ap- 

 pearance in its different forms, 

 to arrive at certain fundamental 

 relations expressed in equations, 

 which are to serve as the basis 

 for calculation, as in conventional 

 physics the dynamical equations 

 formed the starting-point for the 

 various physical theories. In this 

 more radical scheme the quantity 

 " energy " was to play a part similar 

 to that which the quantity " force " 

 played in Newtonian dynamics. 

 This method was probably sug- 

 gested by the novel mode of 

 treatment invented originally for 

 heat - problems by Lord Kelvin 

 and by Clausius, and most strictly 

 adhered to by the former. The 

 isolated character of this classical 

 thermo-dynamics can be got over 

 either by introducing a kinetic 

 hypothesis on the nature of heat 

 or by extending the method of 

 thermo-dynamics to other physical 

 provinces. The former was the 

 most plausible view ; it has its 

 origin in the writings of Rankine 



