310 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



the magnetizing spiral (11), the inclosed needle became strongly mag- 

 netic. Also when the secondary current was passed through the wires 

 of the iron horseshoe (12), magnetism was developed; and when the 

 ends of the second coil were attached to a small decomposing appara- 

 tus, of the kind which accompanies the magneto-electrical machine, a 

 stream of gas was given off at each pole. The shock, however, from 

 this coil is very feeble, and can scarcely be felt above the fingers. 



30. This current has therefore the properties of one of moderate in- 

 tensity, but considerable quantity. 



31. Coil No. 1 remaining as before, a longer coil, formed by uniting 

 Nos. 3, 4 and 5, was substituted for No. 2. With this arrangement, 

 the spark produced when the ends were rubbed together, was not as 

 brilliant as before ; the magnetizing power was much less ; decompo- 

 sition was nearly the same, but the shocks were more powerful, or, in 

 other words, the intensity of the induced current was increased by an 

 increase of the length of the coil, while the quantity was apparently 

 decreased. 



32. A compound helix, formed by uniting Nos. 1 and 2, and there- 

 fore containing two thousand six hundred and fifty yards of wire, was 

 next placed on coil No. 1. The weight of this helix happened to be 

 precisely the same as that of coil No. 2, and hence the different effects 

 of the same quantity of metal in the two forms of a long and short 

 conductor, could be compared. With this arrangement the magnetiz- 

 ing effects, with the apparatus before mentioned, disappeared. The 

 sparks were much smaller, and also the decomposition less, than with 

 the short coil ; but the shock was almost too intense to be received 

 with impunity, except through the fingers of one hand. A circuit of 

 fifty-six of the students of the senior class, received it at once from a 

 single rupture of the battery current, as if from the discharge of a Ley- 

 den jar weakly charged. The secondary current in this case was one 

 of small quantity, but of great intensity. 



33. The following experiment is important in establishing the fact 

 of a limit to the increase of the intensity of the shock, as well as the 

 power of decomposition, with a wire of a given diameter. Helix No. 

 5, which consists of wire only T^jth of an inch in diameter, was placed 



