346 Dr. Woods on the Time required 
whence 
ov=O sin ysin ¢!, 
= =—Osiny(1+c) sing’, 
and 
c= —of(1+c)sinysin ¢’. 
This shows that at any instant the acceleration of the axis 
toward the meridian line of the plane is (1+c)oQ sinysing’. 
The principal axis therefore oscillates about the meridian line 
with the law of the circular pendulum, and the time of vibration 
Tv 
V7 (1+c)oQsiny- 
59 Stanhope Street, Hampstead Road, 
September 19, 1857. 
for a small are is 
XL. On the Time required by Compounds for Decomposition. 
By Tuomas Woops, M.D.* 
te difference between quantity and intensity of a galvanic 
current has been long recognized. The former is generally 
taken to mean the effects produced by the current where no 
obstacle, or the least possible, exists; the latter the electromotive 
force, or its power of overcoming resistance. In order to come 
as near as possible to the cause of different degrees of intensity in 
different galvanic arrangements, let us analyse and compare any 
two; for instance, the usual voltaic pair of two metals and one 
fluid, zine and copper in dilute sulphuric acid, and a Grove’s pair 
consisting of two metals and two fluids, viz. zine acted on by 
sulphuric acid, nitric acid bemg decomposed in contact with 
platina. The electromotive force of the latter is much stronger 
than that of the former; yet the only difference im the chemical 
actions taking place is, that at the platima end of the Grove’s 
nitric acid is decomposed, whilst water is decomposed in the other. 
Now except for this difference, all things in the two arrange- 
ments being the same, if we measure the amount of electricity 
passing from one end to another of each circuit by means of a 
galvanometer, we shall find that the quantity as well as the in- 
tensity of the Grove’s pair is greater than that of the other; the 
needle of the galvanometer will stand at three or four times as 
many degrees with the current of the former as with that of the 
latter. But, as might be expected, if we weigh the zine both 
before and after the current has been passing for the same period 
* Communicated by the Author, having been read at the Meeting of the 
British Association in Dublin, August 26, 1857. 
