520 SPECIAL METHODS OF DISCOVERY. 



will yet be found. 1 Similarly, as the conducting powers of 

 bodies for heat and for electricity appear to obey the same 

 general laws, we may* assume as probable that in any case 

 where there exists an anomalous or exceptional action with 

 regard to the one property, there may be found a similar 

 irregular action with regard to the other. From the 

 truthful hypothesis, that the movement of conducting 

 bodies is retarded by magnetism, it is probable that the 

 flow of saline liquids in vegetables and animals will be 

 found to be retarded between the poles of a powerful 

 magnet. The hypothesis of the intimate correlation of 

 all the physical and chemical powers was one of Faraday's 

 leading ideas during the whole of the latter part of his life. 



c. By assuming that most of the principles which 

 operate in the simpler sciences operate also in the com- 

 plex and concrete ones. The principle of isochronism or 

 rhythm, for example, operates in the vibrations of solids, 

 liquids, vapours, gases, and of the universal ether which 

 pervades all bodies and all space, also in the transmission 

 of sound, light and radiant heat, and probably also in that 

 of electric and magnetic induction. Gruthrie has sug- 

 gested 2 that it also manifests itself in the fact that 

 colloid substances arrest colloids by contact while they 

 are permeable (transparent, diathermanous) to crystalloid 

 substances. The principle of action and reaction, also, 

 we know operates between all the forces of nature, without 

 exception. 



The hypothesis of uniform principles of action may 

 further lead us to imagine the hypothesis that lines of 

 electric force are decomposable, and to ask the question : 



1 Professor Tait has since shown that this molecular and magnetic 

 change is attended by an equally sudden change of thermo-electric 

 capacity. 



2 Philosophical Magazine, September 1876. 



