168 i:lectiiicity« 



ductors this may in some measure be efFected, Hold a 

 r<yd of glass, resin, or sealing wax, towards an electrified 

 body ; and on observing it with an electrometer, you 

 will perceive the alternate zones of opposite electricity. 

 This experiment is known to all philosophers. 



It is needless to remark that we do not now speak of 

 those infinitely minute changes from positive to negative, 

 above spoken of, which, as we have already observed, we 

 Can never hope to distinguish ; but to give a general 

 notionof them, from their operation in these bodies. It 

 ^ight, however, be possible, to describe mathematically 

 the number and properties of these zones. 

 The zones may It is admitted that the foregoing mode of the propaga- 

 conducto^s ^ ^^°" of electricity may be traced on bad conductors, and 

 that it may fevfeti be observed in the air. We have then a 

 right to consider the propagation of electricity as pro- 

 ceeding from undulation ; which may be proved by other 

 experiments. We cannot follow with the electrometer 

 the rapid propagation of electricity on good conductors ; 

 but it frequently leaves traces upon them which confirm 

 the opinion just advanced, 

 —and their If we attempt to melt a long thread of iron by mean^ 

 dT?wire'^^^^°* ^^* ^^^^ charge from the electric battery, we shall quick- 

 ly perceive that one part of the thread is fused, whilst 

 another remains entire, and that these parts are alternate; 

 If a stronger charge be employed, the whole thread Will 

 be fused, and formed into small globules, which are pro- 

 duced by the expansive and contracted zones. The charge 

 tnay be so managed as io give a red he?t to the metal 

 without fusing it ; on which will afterwards appear evi- 

 dent marks of the transition of expansive and contracted 

 zones. 



The foregoing experiments are all Well known to phi- 

 sophers, and afford the strongest proofs of the undulatory 

 propagation of electricity. But if the charge of the bat- 

 tery be augmented to such a degree as to volatilize the 

 iron, and the experiment be so contrived as that the va- 

 pour may be caught upon a sheet of paper, we shall have 

 a complete image of the propagation of electricity, in the 

 clouds described upon the paper by the alternate trans- 

 itions from expansion to Contraction. The thickAcss 



• evtn 



