Baker ian Lecture for 1833. 211 



will also vary. The strength of the magnet, too, will also have 

 considerable influence in determining this point. The funda- 

 mental equation, viz. -rjj- = - — 2 , on which the whole 

 1 sin 2 A. 



rests, having no existence in reality, must vitiate the whole of 

 the mathematical reasoning into which it enters. 



At page 126, the author first discovered th3 necessity of 

 taking into consideration the length of the wire forming the 

 galvanometer coil. In a paper of mine, published in the 

 Journal of the Royal Institution several years ago, I first 

 pointed out the necessity of taking into account the length of 

 the wire forming the coil, which ought to be avoided entirely 

 in investigations of this nature*. But though the author has 

 taken into consideration the length of the coil forming the 

 galvanometer, he has entirely neglected the length of the 

 wire forming the helix. Now it is equally necessary to take 

 into consideration the length of this wire as the length of the 

 other, since the effect has to be communicated through the 

 whole length of the closed circuit. Hence by employing he- 

 lices of the same wire, but of different lengths, the apparent 

 laws of conduction will be found to vary with every new helix 

 which is employed. 



Another source of error has also been overlooked by the 

 author, namely, the breadth of the galvanometer coil. The 

 investigation proceeds on the supposition that the coil is a 

 mathematical line, whereas it may have been an inch broad 

 in that actually employed. The results will therefore vary 

 with the breadth of the coil. 



From certain " aberrations" from the law which had been 

 assumed as the true law, the author suspected, what he might 

 have known from the beginning, viz. that the contiguous coils 

 of the galvanometer acted by induction on each other. After 

 investigating this part of the subject he comes to the following 

 conclusion. " It is therefore clear from all these results that 

 the galvanometer wire acts as a wire of less than its real 

 length, that is, that there is an increase of intensity in it, in 

 consequence of the action of the coils on each other." Now 

 this conclusion is in direct opposition to one of Mr. Fara- 

 day's most beautiful results. That philosopher has proved, in 

 the most satisfactory manner, that when a current is induced 

 on a wire parallel to a conductor, the induced current is 

 always in the contrary direction to the inducing current. 

 The mutual action of the wires forming the galvanometer 

 would therefore diminish the intensity insteadof increasing it. 



The conclusion at which the author arrives is the follow- 



* Journal of the Royal Institution, last series, vol i. (Oct. 1830,) p. 36. 

 2 E2 



