470 Dr. 0. Lodge on an Electrostatic Field 



The importance of the experiment seemed to me (rightly or 

 wrongly) to lie in a possible crucial criterion between Max- 

 wells theory and some of the contemporary German theories ; 

 because it seemed to deal with something less than an open 

 circuit, viz, no circuit at all. 



It also struck me as a sort of converse experiment to that 

 which Prof. Rowland has recently and so successfully carried 

 out : the classical experiment of deflecting a magnetic needle 

 by a rotating charged disk. 



This can hardly be considered a connexion between electro- 

 statics and magnetism, because a static charge in motion, if 

 not a contradiction in terms, is essentially a current ; and 

 what the experiment proves is the truth of MaxwelFs view 

 that all electricity in motion, no matter whether by conduction, 

 displacement, or convection, is a true current, and exerts mag- 

 netic effects. I should rather say that Eowland^s experiment 

 proves the truth of this view of Maxwell so far as convection 

 is concerned. The question of displacement is a ticklish one 

 just now, upon which I shall be safer to be silent*. 



But, now, think of a charged gold leaf hanging between the 

 poles of a magnet. If the gold leaf move it constitutes a 

 current, and therefore at once feels a force uroine; the current 

 (i, e. the hne of motion) across the lines of force in the 

 orthodox way. Instead of supposing the gold leaf to move, 

 let the magnet move. The same thing will happen, because 

 the relative motion is the same as before. (If absolute motion 

 of the static charge through aether is essential, then this last 

 statement falls flat and may possibly be false.) 



If this force were observed, it would be a connexion between 

 magnetism and a static charge, provided any motion of the 

 charged body due to the earth's motion in its orbit were shown 

 to be inoperative or unessential. 



Or, instead of moving the magnet, let its strength be varied ; 

 lines of force pass by the charged body, unless it is symmetri- 

 cally situated, in this case as in the other ; and hence the 

 effect may naturally be expected to be the same in either 

 case. 



The experiment I wished to try was therefore not exactly a 

 converse of the Rowland experiment, but was closely related 

 to it. 



Two years ago my friend Mr. A. P. Chattock came to 



* I say this with reference to what went on at Bath, not with reference 

 to anything that has happened since. This paper was written two or three 

 months ago, before I had heard anything of a communication from Dr. S. 

 P. Thompson to the Royal Society. 



