328 Prof. J. W. Mallet on tlie Weiyltt of a Wire placed 



inovable wire or wires being fixed so far as liorizontal motion 

 is concerned, there would be a lateral swing of the turned- 

 down ends tending to lift them partially out of the mercury ; 

 and to the extent that, by such lifting, copper in mercury 

 was exchanged for copper in air, there Avould of course be 

 increase of effective weight brought to bear upon the balance. 

 But measuring the lengths of the balance-index, arm of the 

 beam, and vertical distance from suspending-ring to surface 

 of mercury in which the wires dipped showed, on very simple 

 calculation, that the amount of vertical motion observed would 

 require, to be thus accounted for, not only a far greater am- 

 plitude of horizontal swing than was actually seen to occur, 

 but much greater than could possibly occur without being 

 arrested by the wires striking the sides of the mercury- 

 cups. 



Thus it appears that in all positions of the suspended wires 

 there was a tendency to upward motion when the current 

 j^assed ; and when the current was from east to west, and the 

 reverse, the apparent gain and loss of weight represented the 

 sum and difference respectively of this tendency with the true 

 vertical component of the earth's action. 



It behoves every one who follows in the footsteps of 

 Faraday, and obtains an experimental result in any way diffe- 

 rent from his, to note carefully in ^^hat respect such dilference 

 may be due to variation of the conditions observed. In this 

 case, beside the experiment having been made at another part 

 of the earth's surface, and with some difference of intensity of 

 the earth's magnetism, the main points in which the experi- 

 ment was varied were these : — 



1. The substitution of several wires for a single one. This, 

 however, is not essential, as the result was verified afterwards 

 with but one wire. 



2. The use of a stronger galvanic current. That employed 

 by Faraday was derived from a single pair of plates of copper 

 and zinc, of the arrangement proposed by Dr. Hare under 

 the name calorimotor ; the size of the plates is not given, or 

 the strength of the acid used; but it is stated that the current 

 •' would barely warm two inches of any-sized wire." One 

 would hardly suppose the external resistance sufficient to 

 make employment of several pairs of plates important ; yet 

 in a repetition of the experiment with a single wire and a 

 Smee's battery of six cells, I found that the effect obtained 

 ^^'as distinct vvith the cells arranged in series, and unobserv- 

 able when they w^ere coupled so as to form but a single 

 pair of plates. 



3. The main reason, however, that Faraday did not obtain 



