256 Mr. R. H. M. Bosanquet on Practical Electricity. 



Let m — n = d as before, 



E 



IfR=*74, d = 3, e=-05, 



ar=5E. 



If we assume E = 1'9, a?=9*'5, wLicli is near enough to 9, 

 the observed value, to snow that we have a general represen- 

 tation of the facts. The constants are not determined with 

 sufficient closeness for accuracy. 



Again, suppose we wish to charge with a larger current. 

 Put <i=4 in the above; then we find for x the balancing cur- 

 rent 14' 6. So that we have only to increase the difference 

 between the two sets of cells. 



Again, supposing we wish to use a smaller current, put 

 d=2. Then x = 6, nearly; or the balancing current is about 

 6 amperes. Both of these conclusions have been verified 

 experimentally. 



With reference to the assumption just made as to the de- 

 pendence of the potential on the current, and generally as to 

 the constants of the accumulator, if we calculate the resistance 

 of a cell of the accumulator from the data available, assuming 

 that the plates are 1 centim. apart, and that the sulphuric acid 

 has a strength even considerably less than 10 per cent., which 

 is its original value, we find a result which is extremely small. 

 In fact, specific resistance* 



•2 per cent. = 4-47 xlO 10 , 

 8-3 „ =3-32xl0 9 . 



The intermediate value 10 10 represents our case with sufficient 

 approximation. 



The edge of each plate is about 30 centim., and its surface 

 not far from 1000 square centim.; so we may consider the 

 conducting solid as consisting of one plate of unit thickness, 

 and surface somewhat exceeding 10,000. 



The resistance therefore would be -ryrj =10 6 , or the thou- 

 sandth of an ohm roughly. This prevents us from assuming 

 that the change of potential caused by current is due to the 

 spread of the tensions along a resistance according to Ohm's 

 law. And it appears probable that any change of tension due 



* These numbers are taken from Prof. E\erett's ' Illustrations of the 

 C.G.S. System.' 



