280 Prof. Norton on Molecular Physics. 



any point of the nearer side eg of the wire. The diminution 

 of the propagated impulse in traversing the wire, simply by 

 reason of the increased length of the passage, as the line is more 

 oblique, should also be a constant fractional part of the impulse; 

 since fc is the same proportional part of af, or an for each point 

 of the wire. Hence the action of any point a of the first wire 

 upon any point / of the second should be inversely proportional 

 to the square of the distance ; and the entire force of action of 

 one indefinite wire upon another should be inversely propor- 

 tional to the distance between the two. (See Lame, Cours de 

 Physique, vol. iii. p. 236.) 



If the currents cross each other under a certain angle instead 

 of being parallel, it may be seen, by attending to the mutual 

 actions of the separate points of the two currents, that there 

 will be attractions or repulsions according to the relative direc- 

 tions of the currents at the points ; and that the entire action 

 will tend to bring the two currents into the same direction, in 

 which the attraction will be a maximum. 



External Action of an Electric Current upon bodies in their 

 natural state. — In undertaking to deduce from our fundamental 

 principles the varied phenomena of the action of a current upon 

 bodies in its vicinity, we have to consider that there are two 

 modes in which the external impulsive force of a current may 

 act upon such bodies and develope currents, — the one direct, and 

 the other indirect. (1) The propagated impulses may take 

 effect directly upon the atoms of the electric atmospheres of the 

 molecules, impelling them in the same direction that the primary 

 current is moving, and so tend to generate a current similar to 

 the primary. (2) Or these same sethereal impulses may fall 

 upon the central atoms of the molecules, force up the atmo- 

 spheres on the side of the atoms upon which they fall, and so 

 develope a current opposite to the original one. We have to 

 consider also that theoretically the external current-force may 

 operate in both these ways, either upon the simple molecules 

 which are grouped together into compound molecules, or upon 

 compound molecules as a whole. The action upon the constituents 

 of the compound molecules tends to develope currents within 

 the mass of these molecules. Among the variety of especial 

 currents which may thus be excited, we have particularly to 

 note those which may be developed in the surface of each group, 

 and circulate around it from particle to particle. If the direct 

 mode of operation of the primary current predominates, such 

 circular currents are magnetic; if the indirect prevail, they are 

 diamagnetic. If the two tendencies countervail each other, the 

 substance is in a neutral magnetic condition. The neutral mag- 

 netic state may also result from the absence of groups of parti- 



