216 Contributions to Electricity and Magnetism. 
hibited in Fig. 3, with the exception that in this the compound 
helix is represented as receiving the induction, instead of coil 
o. 2. 
29. When the ends of the second coil were rubbed together, 
a spark was produced at*the opening. When the same ends were 
joined by the magnetizing spiral (11,) the inclosed needle became 
strongly magnetic. Also when the secondary current was passed 
through the wires of the iron horse-shoe, (12,) magnetism was 
developed ; and when the ends of the second coil were attached 
to a small decomposing apparatus, of the kind which accompa- 
nies 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 moder- 
ate intensity, 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 ar- 
rangement, the spark produced when the ends were rubbed to- 
gether, was not as brilliant as before; the magnetizing power Was 
much less; decomposition was nearly the same, but the shocks 
were more powerful, or, in other words, the intensity of the indu- 
ced current was increased by an increase of the length of the 
coil, while the quantity was apparently diminished. 
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 appar 
tus 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 impU- 
nity, except through the fingers of one hand. A cireuit of fifty 
six of the students of the senior class, received it at once from 2 
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 intensity. 
33. The following experiment is aaa in establishing the 
fact of a limit to the increase of the intensity of the shock, % 
