of Steel Needle-Points in A 



ir. 



297 



together by internal charges, they maybe represented thus in 

 their free state : — 



A B 



C D 



fir 



E F 



the lines between the pairs of atoms signifying lines of 

 electrostatic force. A chain of such molecules will give way 

 when it is put in a field of force just strong enough to redis- 

 tribute the charges by induction so that half as many lines 

 pass between A and B, C and D, &c. as before ; and the 

 remainder pass between B and C, D and E, &c. This state 

 of things may be represented thus : — 



Put in another way, the strength of the field which will do 

 this is rather greater than that which would induce on each 

 of the two end atoms of the chain half their assumed initial 

 charges, supposing them to be connected by a fine conducting 

 wire. It depends thus on the length of the chain, being 

 greater as the chain is shorter. 



In the case (b), a constant cohesive affinity between the 

 two parts of the molecule, it is necessary to suppose that elec- 

 tricity can pass from one to the other under the influence of 

 induction when they are put in a field of force, in order that 

 after separation they may be oppositely charged. The fol- 

 lowing figure shows a chain of such molecules on the point of 



breaking down, the break occurring when the cohesive forces 

 (^wwwv) are just overcome by the electrical forces (==^) set 

 up by the field. Here, again, the longer the chain the weaker 

 the field required to break it ; and as the cohesive forces are 

 constant, and the electrical forces are dependent, for given 

 molecular arrangement, only on the charges induced in the 

 molecules, it follows that these charges will also be practically 

 constant, no matter what the length of the chain may be. 



In both these cases, therefore, for all lengths of chain, the 

 atomic charges at the breaking-point are constant ; in case (b) 

 being rather less than such as would be induced by the field 

 on the end atoms, supposing the latter to be connected by a 

 conductor ; and in case (a) less than twice that amount (less, 

 because the chain is not a continuous conductor). Their 



Phil. Mag. S. 5. Vol. 32. No. 196. Sept. 1891. X 



