Experiments with Open Circuits* 51 



if we always go round the coil in the same direction. Now 

 when the coils are arranged according to the scheme 

 ABCDEF, two neighbouring windings of the coil can differ 

 at most in their potentials by the rise in potential due to one 

 layer of the wire ; but when the coils are arranged according 

 to the scheme AB — DCEF, the last layer of the first coil 

 differs from the first layer of the second by the rise in poten- 

 tial due to the whole length of the second coil, or by the rise 

 due to about 100 yards of wire. Thus in this case we have 

 two places of very different potential near together ; in other 

 words, we have the condition necessary for a condenser of 

 large capacity. The consequence of the coil possessing this 

 electrostatic capacity, is that when the electromotive force 

 produced by the breaking of the current on the primary acts 

 upon it, the electricity is distributed in lumps, as it were, along 

 the coil, being lumped up in the places of great electrostatic 

 capacity. In consequence of this irregular distribution of the 

 electricity, electrical oscillations, which will last until destroyed 

 by the resistance of the wire of the coil, are set up, just as in 

 a canal, if the water be heaped up in some places and de- 

 pressed in others, the water does not sink at once to rest, 

 but oscillates until the oscillations are destroyed by friction. 

 The motion of the electricity during these electrical vibra- 

 tions will constitute a current through the coil which will 

 magnetize the needle. 



The fact that the magnetism produced in a needle placed 

 in the magnetizing-spiral is different when the spiral is 

 placed in different parts of the secondary circuit, the ar- 

 rangement of coils in the secondary remaining the same, 

 shows that the current is not the same all along the secondary. 

 If this be the case, the electricity must accumulate on the 

 wire of the coil ; and consequently the coil must act as a con- 

 denser. This was strikingly shown in the experiments referred 

 to above, when, with the coils arranged according to the 

 scheme AB — DCEF, the needle vibrated 29 times per minute; 

 whilst with the arrangement ABDOEF — it only vibrated 3 

 times per minute. It is also well shown in the folio wing- 

 case: with the coils arranged according to the scheme 

 AB — DCEF, 29 vibrations per minute were produced ; but 

 if the magnetizing-spiral was placed between C and E instead 

 of B and D, so that the arrangement was that denoted by 

 ABDC — EF, only 15 vibrations per minute were produced. 



It is not necessary in these experiments to have three 

 secondary coils; many of the effects can be produced with two, 

 as in the following experiments. The ends E and F of the 

 third coil were joined, so that it was altogether out oi' the 



E2 



