216 Contributions to Electricity and Magnetism. 



hibited in Fig. 3, with the exception that in this the compound 

 hehx is represented as receiving the induction, instead of coil 

 No. 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, andean 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 appara- 

 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 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 



