to Electricity and Magnetism. 495 



making and breaking a galvanic current*. And in connexion 

 with this part of the subject, I will first mention a fact which 

 was observed in the course of the experiments given in the 

 last section, on the direction of the induced currents of dif- 

 ferent orders. It was found, that though the indications of 

 the galvanometer were the same as those of the spiral, in re- 

 ference to the diiection of the induced currents, yet they were 

 very diff'erent in regard to the intensity of the action. Thus, 

 when the arrangement of the apparatus was such that the in- 

 duction at making the battery circuit was so feeble as not to 

 give the least magnetism to the needle, and so powerful at the 

 ending as to magnetize it to saturation, the indication of the 

 galvanometer was the same in both cases. 



42. Also, similar results were obtained in comparing the 

 shock and the deflection of the galvanometer. In one expe- 

 riment, for example, the shock was so feeble at making con- 

 tact that it could scarcely be perceived in the fingers, but so 

 powerful at the breaking of the circuit as to be felt in the 

 breast; yet the galvanometer was deflected about thirty-five de- 

 grees to the right, at the beginning of the current, and only an 

 equal number of degrees to the left, at the ending of the same. 



43. In another experiment, the apparatus being the same 

 as before, the magnetizing spiral and the galvanometer were 

 both at once introduced into the circuit" of the helix. A 

 sewing needle being placed in the spiral, and the contact with 

 the battery made, the needle showed no signs of magnetism, 

 although the galvanometer was deflected thirty degrees. The 

 needle being replaced, and the battery circuit broken, it was 

 now found strongly magnetized, while the galvanometer was 

 only moved about as much as before in the opposite direction. 



44. Also, eflfecls similar to those described in the last two 

 paragraphs were produced when the apparatus was so ar- 

 ranged as to cause the induction at the beginning of the bat- 

 tery current to predominate. In this case the galvanometer 

 was still nearly equally affected at making and breaking bat- 

 tery contact, or any difference which was observed could be 

 referred to a variation in the power of the battery durin^r the 

 experiment. 



45. Another fact of importance belonging to the same class 

 has been mentioned before (24.), namely, that the actions of 

 the currents of the tliird, fourth, and fiftii orders produce a 

 very small effect on the galvanometer, compared with that of 

 the secondary current; and this is not alone on account of the 

 diminishing power of the successive inductions, as will be evi- 

 dent from the following experiment. By raising the helix from 



* Sec iiiy last ijai>er in Loiul. and Edinb. Hiiii. Mag., March 1840, p. 200. 



