90 



SCIENTIFIC THOUGHT. 



processes going on in the neighbourhood of electrically 

 charged bodies, of electric currents, of magnets and 

 diamagnets, can be visualised. 1 For didactic purposes 

 such elaborate models may prove to be of great value, 

 though as a true mechanical basis of a physical theory of 

 natural processes they have to be received with caution. 

 None of those physicists who have expended their ingen- 

 uity in devising these contrivances seem to attach more 

 than a symbolic or ideal value to them : they have, how- 

 ever, the desired effect of producing on the mind of the 

 learner, of the practical inventor, or of a popular 

 audience a strong conviction that all physical phenomena 

 can be described as processes of motion, and that the 

 ultimate solution of the problem of natural philosophy is 

 to be found in a kinetic or mechanical view of pheno- 

 mena. Physics and chemistry are, according to this 



1 Such illustrations may be found 

 in Dr Oliver Lodge's ' Modern 

 Views of Electricity,' a book which 

 has had a large circulation and has 

 helped to diffuse cori-ect and practi- 

 cally useful ideas on electric and 

 magnetic problems and phenomena. 

 There is a danger of such mechani- 

 cal illustrations becoming too rigid 

 and of their being taken too literally ; 

 still, for the purposes of practical 

 application and handling it is indis- 

 pensable to possess some mechanical 

 mode of representation and con- 

 struction by which actual problems 

 can be readily solved. The success 

 of Dr Lodge's attempt both in this 

 country and on the Continent, 

 especially in Germany, proves suf- 

 ficiently that it meets a much-felt 

 want. See inter alia Prof. Rosen- 

 berger's five lectures, ' Die moderne 

 Entwickelung der elektrischen Prin- 

 cipien,' Leipzig, 1898, p. 133. A 



great authority abroad, Prof. Lud- 

 wig Boltzmann, has made use of a 

 peculiar kind of mechanical motion, 

 investigated by Helmholtz, to il- 

 lustrate electrical phenomena. Th& 

 characteristic of such motion 

 which is termed cyclic is this, 

 ' ' that in the place of every particle 

 which changes its position, an equal 

 and equally moving particle enters, 

 so that the condition of the system 

 during the motion is nowise al- 

 tered " (' Vorlesungen iiber Max- 

 well's Theorie,' Leipzig, 1891 and 

 1893, vol. i. p. 14). Cycles can be 

 " coupled," &c. The general dyna- 

 mical relations of such cyclic 

 systems are investigated, and by 

 introducing the necessary restric- 

 tions, based upon experimental 

 facts, and suitable hypotheses 

 facts and hypotheses being clearly 

 distinguished the general equa- 

 tions of Maxwell are arrived at. 



