﻿Fit z Gerald Lore ntz Contraction. 01 



by s 1? and with the field corresponding to that motion (i.e. with- 

 out other charges or fields constraining it to do so), we should 

 find the operation impossible. When we speak of separating 

 the charge out in this way, we must imagine the ope ration to 

 be performed entirely by electromagnetic agency, the very 

 atoms of our imaginary fiugers are parts of the electro- 

 magnetic system, and the action of separating the electron 

 out is one which must be supposed to have been antioipated 

 in the system for an infinite time back, and to have arisen 

 out of the spontaneous changes in the system as a whole. 



Again, we should find it impossible to imagine a set of 

 actual spontaneous electromagnetic changes, by wdiich the 

 fields of the two electrons moving along the axis of x in the 

 example above quoted could be brought into the state there 

 suggested after all other fields had been removed, at least, if 

 we did find it possible to get them into this state, from an 

 actually existing state, it would mean that the electromagnetic 

 equations were inconsistent with facts. If we inquire why it 

 is that, of all the conceivable states of electronic motions 

 satisfying the electromagnetic scheme only certain types are 

 found in practice, the electromagnetic equations have nothing 

 to tell us. If we give them an actual system to manipulate, 

 they can tell us its subsequent and previous hi-tory, but they 

 are unable to tell us, for example, why it is that two electrons 

 when alone cannot continually follow each other with constant 

 velocity, or why a single electron cannot move by itself in a 

 closed curve. 



Of course, in other branches of physical knowledge we 

 form other laws, founded on experiment, which specify more 

 precisely the types of motion which can exist ; for instance, 

 laws of motion involving the conception of forces between 

 point singularities would tell us that the above system of two 

 point charges following each other with constant velocity was 

 an impossible one. Again, the tangential surface condition 

 introduced in the consideration of problems on charged con- 

 ductors, involves a restriction on the types of field which can 

 occur, affording as it were a means by which one body can 

 act on another. A few remarks must here be made on the 

 position occupied by these u Subsidiary Laws," as we shall call 

 them, in a scheme which takes the electromagnetic equations 

 as a basis. 



If at some instant we were given the complete field at every 

 point in the universe, we should require no subsidiary laws at 

 all, the electromagnetic equations are themselves sufficient, as 

 we have already remarked, to tell its the complete past and 

 subsequent history of the system, every action and even 



