﻿deduced from the Elect need Theory of Matter. f>7 



Thus all the x components on a are the same as before, so 

 that i£ they balanced out before the motion, they will still 

 balance out, and while the y components are not the same as 

 when the system was at rest, they are all altered in the same 

 ratio, so that if they balanced out before the motion was 

 imparted, they will balance out when the body is moving, and 

 a similar remark applies to the z components. Hence, the 

 whole system will again be in equilibrium if it shrinks in this 

 manner, and suitable constraints are applied at the boundary. 

 We must now pass on to the consideration of systems in 

 which the electrons are in motion, even though the system 

 as a whole is at rest. We may remark at once that the final 

 state of such a system when set in motion with velocity v 

 cannot be absolutely asserted without knowledge of the means 

 by which that velocity is brought about ; we know, as a 

 matter of fact, that if we set a piece of lead, for example, in 

 motion with a blow, the final condition of that lead will be 

 different to what it would have been if it had gained its 

 velocity gradually, the lead will be deformed by the blow, 

 and though it may at first sight be thought that we are here 

 introducing other considerations which ought not to be 

 involved, we must I think admit them, for after all, our piece 

 of lead is to be looked upon as simply an electromagnetic 

 system, and on our present view, both the blow and the 

 steady method of imparting the motion are means of pro- 

 ducing the final velocity v, which, if our knowledge were 

 sufficiently great, could be expressed completely as the result 

 of certain external electromagnetic effects. The final state 

 of the electronic motions is not, however, entirely dependent 

 on the method of producing the velocity, the state is restricted 

 by the final velocity v imparted, so that it is not unreasonable 

 to suppose that if no sudden impulse is given to certain of 

 the electrons, if all, so to speak, are acted on at once, the 

 final state of motion of the electrons in the moving system 

 will be sensibly independent of slight modifications in the 

 method of producing the motion. If then we find a system 

 in motion as a whole with velocity v, the relative motions of 

 whose electrons are consistent with the electromagnetic laws, 

 and which differ from those in the system at rest by amounts 

 which get smaller and smaller, the smaller we make v, we 

 may with a certain amount of confidence assert, that this 

 is the system which the fixed system becomes when set in 

 motion ; this in fact is all that we can do without specific 

 knowledge of the electronic motions, it is all that ever has 

 been done, or can be done by any other method of considering 

 the matter. 



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