52 Mr. J. Parnell on Secondary Currents 



oscillatory motion, there is any constant current produced by the 

 moon's force. Now, as the circumstances about the four points 

 of equilibrium are precisely similar as long as the ocean is sup- 

 posed spherical, we may assume that the relative velocity of the 

 water at equal distances from each of these points is the same, 

 the points of no relative velocity being e, f, g, h. This is equi- 

 valent to supposing that the mean movement of rotation of the 

 ocean does not differ ab initio from that of the earth. Tn this 

 case, then, the retardation between e and /is exactly balanced 

 by the acceleration between / and g, and similarly in the other 

 two quadrants. But when the ocean has assumed the form of an 

 ellipse this symmetry ceases. As the tangential force is, cceteris 

 paribus, proportional to the distance of the particles attracted 

 from the centre of the earth, it follows that the forces are greater 

 from e to /and from g to h than from/ to g and from h to e. 

 Therefore the retardation in the former intervals is not completely 

 compensated by the acceleration in the latter. Hence there is a 

 balance of retardation, in other words, a continuous current, re- 

 latively to the earth, westward. 



IV. Friction being taken into account, the effect of this is to 

 retard the earth's rotation, or to lengthen the day. 



VIII. On Secondary Currents and a new Secondary Battery. 

 By John Parnell, M.A., F.R.A.S* 



1. i S far as I am aware, no account has hitherto been pub- 

 -^^- lished of the employment of alkaline solutions in the 

 development of secondary currents ; the investigation described 

 in this paper was therefore undertaken for the purpose of ascer- 

 taining whether by this means effects more powerful than those 

 previously observed could be obtained ; and the results appear to 

 be satisfactory. 



2. The apparatus employed consisted of: — 



(a) A Daniell cell as an exciting couple, connected with an 

 ordinary commutator. 



(b) The experimental secondary couple, which was formed of 

 two plates of the same metal, one of which was folded round the 

 other in a U-form. These two plates were separated from one 

 another by pieces of ebonite at a distance apart of about 2 mil- 

 lims. The available surface of the inner plate was nearly 14 

 square centimetres. 



(c) A Morse key, by which one pole of the secondary couple 

 could be rapidly detached from the exciting cell and thrown into 

 communication with 



* Communicated by the Author. 



