[ 136 ] 



XX. On certain Phanomena of Electrical Discharge. 

 By Sir W. Snow Harris, FJIS. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



I HAVE duly considered Dr. Riess's notice of my memoir in 

 your May Number, " On Electrical Discharge/' I regret 

 exceedingly that it should have been treated by Cr. lliess in so 

 dictatorial and intolerant a spirit. It will be my endeavour, 

 however, in the few concluding observations I have to make, to 

 avoid every thing calculated to provoke angry discussion, and 

 confine myself strictly to facts and to the scientific merits of 

 the question at issue between us, without any discourteous com- 

 ment on the several personal animadversions and reflections on 

 me, in which Dr. Riess has thought fit to indulge. 



Dr. lliess says that 1 had " long since set up a law upon the 

 dependence of the electrical heat upon the charge of the bat- 

 tery,'' and that he " ascertained this law to be incorrect, and set 

 up another in its place." All this, however, as it here stands, is 

 mere assertion, worth nothing as scientific evidence in reply to 

 the facts and phcenomena set forth in my memoir. According 

 to my view of the question, Dr. Riess has quite failed in his 

 demonstration, which I conscientiously believe to rest entirely 

 upon defective hypothetical assumptions, at variance with the 

 known laws of ordinary electrical action. The essence of what 

 I advanced and what I still maintain is this, that you cannot ex- 

 tend your electrical battery by adding to the number of its jars, 

 without at the same time increasing the resistance to the subse- 

 quent discharge of the accumulation ; consequently a given quan- 

 tity of electricity will experience more resistance when discharged 

 from an increased number of jars, than when discharged from a 

 smaller number ; so that you cannot take the resistance as con- 

 stant. But, as I have shown, if you extend your battery-surface 

 without division, as in accumulating the charge upon a very large 

 jar instead of a very small jar, then in using the same charging rod 

 you have the resistance nearly the same in each ; now in this case 

 you find the effect on the wire of the thermo-electrometer invari- 



able. What then becomes of Dr. Riess's formula F=— , taking 



s to indicate the increased surface ? Why the surfaces may be 

 as 1 : 2, and yet the effect of the discharge of a given quantity 

 of electricity the same. According to Dr. Riess, the density 

 of the accumulated electricity would be in such a case twice as 

 great in the small jar ; so that if the effect were as he says, " pro- 

 portional to the product of the quantity by its density," the 

 same quantity discharged from a jar of half the surface should 



