Magnetism and the Trade Winds. 291 



fifteen wires, the second winding is only wound with four- 

 teen threads, whilst the fifteenth is carried along the axis, 

 &c. ; consequently every convolution of the fifteen windings 

 have a thread less, and the ends of all the other threads have 

 direction of the axis. The ends of the fifteen threads are 

 soldered in the middle, and the two thick wires without 

 touching each other, are so bent that they can be suspended 

 in the little cups of the apparatus of Ampere, then a current 

 passing through the spiral will divide itself in such a man- 

 ner that it is most strong on the external ends of the spiral 

 but decreases more and more to the middle. If the windings 

 of the spiral took place in the direction of the hand of a 

 watch, then the end of it where the current enters will be- 

 come a south pole, but a north pole kept parallel to the spiral 

 will repel it, only the final convolution will be attracted, 

 and it represents the disengaged magnetism of the final sur- 

 face. 



*' A second spiral is wound like that described only with 

 this difference that the strongest convolutions are in the 

 middle, and the feeblest near the ends. This spiral will be 

 attracted by the north pole of a magnet over the half in 

 which the current moves at first or enters, but the other 

 half will be repulsed by it. The third spiral has the winding 

 the same strength over the whole extent ; it is indifferent to 

 a magnet pole which is not too near, and only the final con- 

 volutions are attracted or repulsed. 



" Therefore it is permitted to enlarge the theory of Am- 

 pere in this manner : — 



" — If an electric current passes through a spiral in the 

 direction of the hand of a watch, and, 



" a If the current is more feeble in every winding as it is 

 nearer to the centre of the spiral, then that half is attracted 

 by a south pole in which the current enters except the first 

 winding. 



" b But if the current is stronger in every winding as it is 



nearer to the centre of the spiral, then that half is repulsed 



by a south pole in which the current enters, including the 



first winding. 



K " The contrary will be the case for that half in which the 



