94 CORRELATION OF PHYSICAL FORCES. 



and electricity appears to have led Coleridge to parallel it by 

 the transverse expansion of matter, or length and breadth, 

 though he injured the parallel by adding galvanism as depth ; 

 whether a third force exists which may bear this relation to 

 electricity and magnetism is a question upon which we have 

 no evidence. 



The ratio which the attractive magnetic force produced 

 bears to the electric current producing it has been investigated 

 by many experimentalists and mathematicians. The data are 

 so numerous and so variable, that it is difficult to arrive at 

 definite results. Thus, the relative size of the coil and the 

 iron, the temper or degree of hardness of the latter, its shape, 

 Or the proportion of length to diameter, the number of coils 

 surrounding it, the conducting power of the metal of which 

 the coils are formed, the size of the keeper or iron in which 

 magnetism is induced, the degree of constancy of the battery, 

 &c., complicate the experiments. 



The most trustworthy general relation which has been 

 ascertained is, that the magnetic attraction is as the square of 

 the electric force ; a result due to the researches of Lenz and 

 Jacobi, and also of Sir W. S. Harris. 



Lastly, electricity produces chemical affinity ; and by its 

 agency we are enabled to obtain effects of analysis or syn- 

 thesis with which ordinary chemistry does not furnish us. Of 

 these effects we have examples in the brilliant discoveries, by 

 Davy, of the alkaline metals, and in the peculiar crystalline 

 compounds made known by Crosse and Becquerel ; though 

 the latter are probably not always the definite result of the 

 electric current, but are formed by the chemical changes 

 produced by its bringing the molecules of the substances 

 experimented on within the range of aggregation. 



