212 Mr W. S. HARRIS on the Heat excited i\ 



in 



states, " That in a battery where the quantity of electricity is 

 very great, and the intensity very low ; charcoal, made to touch 

 only in a few points, is almost as much an insulating body as 

 water, and cannot be ignited, nor can wires of platinum be heated 

 when their diameters is less than the Vtfi of an inch, and their 

 length 3 or 4 feet ; and a foot of platinum- wire is scarcely heated 

 by such a battery ; whilst the same length of silver-wire is made 

 red hot, and the same lengths of thicker wires of platinum are 

 intensely heated." In this case, it is evident that the superior 

 conducting power of the silver allows the quantity of electricity 

 to pass through it, necessary to complete the heating effect ; 

 whilst the inferior conducting power of the platinum impedes 

 the transmission of the charge ; so that the heating effect is only 

 evinced on thicker wires. 



11. I endeavoured to find, by a variety of experiments, whe- 

 ther, on increasing the dimensions of the wires in the electrome- 

 ter, any ratio greater than that of the increased power could be 

 obtained, but I did not arrive at any new result. It is, however, 

 not unlikely, that, provided the times of transmission were in- 

 versely proportional to the quantities of electricity transmitted ; 

 that is to say, if, in one-half the time, twice the quantity was dis- 

 charged, and so on, then the indications of the electrometer 

 might possibly be in a higher ratio, as I have invariably observed 

 in the case of ordinary electrical explosions, by means of coated 

 jars, in which the intensity of the action is such, that the whole 

 accumulation is forcibly transmitted through the wire, in a dense 

 form *. 



12. Much care is requisite, in speculating on these curious 

 phenomena, which appear to be intimately connected with the 

 relations subsisting between the causes of heat and electricity ; 

 nevertheless the view taken by the celebrated philosopher above 



* Memoirs of Plymouth Institution, p. 68. and 84. 



