to Electricity and Magnetism. 207 



30. This current has therefore the properties of one of mo- 

 derate intensity, but considerable quantity. 



31. Coil No. I 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 mag- 

 netizing power was much less ; decomposition was nearly the 

 same, but the shocks were more powerful, or, in other words, 

 the intensity of the induced current was increased by an in- 

 crease of the length of the coil, while the quantity was ap- 

 parently decreased. 



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

 and therefore 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 magnetizing 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 in- 

 tense 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 Leyden 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 y^jth of 

 an inch in diameter, was placed on coil No. 2, and its length 

 increased to about seven hundred yards. With this extent 

 of wire, neither decomposition nor magnetism could be ob- 

 tained, but shocks were given of a peculiarly pungent nature; 

 they did not however produce much muscular action. The 

 wire of the helix was further increased to about fifteen hun- 

 dred yards; the shock was now found to be scarcely percep- 

 tible in the fingers. 



34. As a counterpart to the last experiment, coil No. 1 was 

 formed into a ring of sufficient internal diameter to admit the 

 great spool of wire (11.), and with the whole length of this 

 (which, as has before been stated, is five miles) the shock was 

 found so intense as to be felt at the shoulder, when passed 

 only through the fore-finger and thumb. Sparks and de- 

 composition were also produced, and needles rendered mag- 



