338 



MR. W. DUDDELL, ON THE KESISTANCE AND 



length varied ; and in order to increase the accuracy of the equation some extra 

 results were obtained in which both current and length have been varied. 



On attempting to find the constants a, ft, y, 8 to fit all these values, the first 

 difficulty encountered was that, assuming the current to be constant and the length 

 varied, Mrs. AYRTON'S equation required the P.D. to be a linear function of the 

 length ; a glance at Curve V. shows that this was not even approximately true for 

 these carbons and the long range of lengths from 1 millim. to 30 millims. used. At 

 first it was thought that this might in some way be due to the kind of carbons used 

 in the experiments. The connection between P.D. and length for constant current 

 was, therefore, determined for the same size and make of carbons used by Mrs. 

 AYRTON in her experiments* ; the results are given in Curve VII. 



<Spi- 



80 



I 



o 



a: 



cute 



Beti teen 



P.O. 



and 



Lei 



Solid Arc 



40 



Spos lie 1 ' C arlx ns 

 _3ire 



4hiQugt 



cer 

 Arc 



30 



o I 2 3 4 5 6 7 8 9 IOIII2I3I4I51&I7l8i920ZI222324252&272S2330 



Arc Length. 



In the curve the straight line represented by Mrs. AYRTON'S equation is also given. 

 The divergence between the P.D.'s calculated from Mrs. AYRTON'S equation and ihe 



* The ' Electrician,' 1895, vol. 35, p. 420. 



