350 Mr. 11. Murphy on Electrical Injluencc. 



Set, No. 6. — With a maintaining power of 5 pounds weight. 



•c, . Loss in Extent of 



Experiments. ^ ^^ Vibration. 



With hair — 2 ra 7*5 S 1-8° 



Ditto —2 7*2 



Without hair —2 6'0 2'0 



The loss of 1 second in the rate of the pendulum arising from 

 the increase of friction in consequence of its slight contact 

 with the hair, may be explained as follows : The impulse given 

 to the pendulum was all during its ascent; this caused all the 

 friction that would affect the time to be in its descent. Since 

 the friction in its ascent would fall into the impulse, it would 

 occasion a diminution of its power only, but have no effect on 

 the time of the ascent; it would, however, have its full effect 

 on that of the descent, and produce the loss of 1 second, as 

 shown by experiment. 



[To be continued.] 



LVII. On the Mathematical Laws of Electrical Influence. By 

 R. Murphy, Esq. M.A. Fellow of Cains College, Cambridge*. 



E W exact results, in the mathematical sense of the word, 



F 



have been obtained with respect to the distribution of 

 electricity when any number of electrized bodies mutually in- 

 fluence each other. M. Poisson has established a very simple 

 principle for reducing such problems to analysis, and another 

 may be announced by assuming the influences to be consecu- 

 tive : thus if two spheres A and B mutually influence each 

 other, we may suppose, first, that A alone influences B ; se- 

 condly, that the disturbance thus produced in B influences A, 

 and so on : by this means we may arrive at the final distri- 

 buion of electricity on the surfaces of A and B. — The fol- 

 lowing exact results of influencing bodies may be noticed. 



If any number of concentric shells, the thickness of any one 

 of which is uniform, are charged with electricity, the quantity 

 of electricity developed on the outer surface of any shell will 

 be the sum of the charges of all the interior shells, including 

 the individual shell itself; and on its inner surface, the same 

 i>um excluding that shell. 



If a very remote body influence an electrized sphere, the 

 section made by a plane through its centre perpendicular to 

 the direction of the disturbing force, will contain those points 

 on the surface which are not influenced, and the influence at 



* Communicated by the Author. 



1 



