4^8 REPORT^18G9. 



A small Grove's battery was employed to send a current through the three 

 coils and the secondary coil of the galvanometer Gr^. 



Equilibrium of the electric balance was obtained by working the micro- 

 meter, and so adjusting the distance of the disks. At the same time equili- 

 brium of the galvanometer was obtained by altering the resistance of the 

 shunt S. 



The simultaneous values of the micrometer and the shunt formed the result 

 of each experiment. It was necessary also to ascertain the ratio of the mag- 

 .netic effects of the two coils of the galvanometer immediately after each set 

 qf experiments. 



: The method of experimenting appeared capable of considerable accuracy ; 

 but some difficulties arose from want of constancy in the batteries, from 

 leakage of electricity, &c., so that many of the experiments were known to 

 be faulty. Twelve experiments, however, against which nothing could be 

 proved at the time of making them, in which the distance of the disks 

 ranged from | to | an inch, and the power of the batteiy from 1000 to 

 2600 cells, gave values of v of which the least was 2S"4, and the greatest 

 29-4 Ohms; and in nine of these the values lay between 28-68 and 28"91. 

 The mean of the 12 Avas — 



r> = 28-798 Ohms. 

 = 288,000,000 metres per second. 

 = 179,000 statute miles per second. 



This result is much low-er than that of MM. Weber and Kohlrausch, 

 which was i' = 310,740,000 metres per second, but agrees, I believe, more 

 nearly with values recently obtained by Sir W. Thomson, whose method, as 

 well as mine, depends on the B.A. unit. Weber's method depends on the 

 measure of capacity. It is to be hoped that this important physical quan- 

 tity ma)^ soon be determined by methods founded on capacity, and disem- 

 barrassed from the phenomena of " electric absoi-ption," whicli occurs in all 

 solid condensers, and which would tend to give too high values of v. 



