OF WIRES FOR ELECTRICITY- 



SSI 



consequently 



_ 2 • cos ^ (ax + «(x)' sin \ (ax — «(j)X 

 — sin i a(j.) 



Having in this manner found out m for the end of the series of experi- 

 ments, the correction of other angles became easy by multiplying the 

 sines of their halves respectively by 



In this manner the angles of deviation of the 2nd column of the follow- 

 ing table are calculated. 



Angles of Deviation 



observed, calculated. 



Difference. 



Without an J' interposed wires ... 

 With interposed wires 7 feet long 

 14 



21 



28 

 35 



80-60 

 48-96 

 35-60 

 28-09 

 23-07 

 19-73 



80-53 

 49'0& 

 35-62 

 28-03 

 23-12 

 19-69 



-0-07 

 + 0-12 

 + 0-02 

 —0-06 

 + 0-05 

 —0-04 



The 3rd column is calculated entirely according to the above for- 

 mulae (A). The smallness of the differences of the 4th column proves 

 likewise the correctness of the proportionality of the conducting resist- 

 ances to the lengths of the wires. The following values were obtained 

 for X and 3/ : 



X = 12-583 7/ = 8-133. 



X was according to the previous calculation = 12-539, the difference 

 therefore of the resistances was only =: 0*044 of an English foot : y con- 

 siderably differed from the preceding value, the electromotive spiral 

 having here two coils less. 



Passing now to experiments which are to indicate the proportion of the 

 conductibility with reference to the diameters of the wires, I must pre- 

 viously observe, that the difficulty of obtaining accurately agreeing re- 

 sults is here far greater than in making experiments with wires of the 

 same diameter though of different lengths. The reason of this is the 

 difficulty of obtaining wires of different diameters quite equal in every 

 other quality. Should we, for instance, take copper wires of different 

 thickness as they are sold in shops, we should then obtain entirely dif- 

 ferent results. I once obtained two copper wires, of which that having 

 the greater diameter was a worse conductor than that which was thinner, 

 contrary to all previous approved experiments, all observers agreeing 



