a7ul on certain Principles in Electrical Science, 469 



We have seen how little support Mr. Sturgeon derived 

 from Lord Mahon ; he obtains still less from Priestley, who, 

 without any compromise, svveeps away his whole theory. 

 Lord Stanhope and Dr. Priestley, eminent amongst the phi- 

 losophers of their day, will be doubtless admitted to be as 

 good authority as Mr. Sturgeon. 



15. The second kind of lateral discharge is, we are in- 

 formed, "a radiation of electric matter from conductors carry- 

 ing the primitive discharge." It takes place, the author says, 

 from edges, and that hence " sharp edges of metal carrying a 

 flash of lightning would discharge necessarily a great quantity 

 of fluid into neighbouring bodies." No author is pressed into 

 the service on this occasion, and for the best possible reason, 

 no accredited writer has ever treated of such a phienomenon 

 as applying to a lightning rod. It is in fact applicable only to 

 charged conductors. Thus ragged or pointed rods attached 

 to the prime conductor of the electrical machine exhibit brushes 

 of light, whilst other similar bodies, within their influence, 

 have the appearance of stars. The lights on steeples, and on 

 the sail yard and masts of ships, mentioned by Pliny, are of 

 this 'kind. Franklin explained these phasnomena, and showed 

 that pointed bodies were favourable to the rapid dissipation of 

 electrical accumulations, and, as is well known, availed himself 

 of the important fact in his application of the pointed lightning 

 rod. How Mr. Sturgeon has contrived to associate this ef- 

 fect with the effects of discharges of lightning through conduct- 

 ors it is difficult to say. It is certainly a very strange con- 

 fusion of things. That the effect in question has nothing to 

 do with a sharp or round edge, or angular discharges, may be 

 shown by the following experiments : — 



{u). Dr. Priestley discharged a battery over a wire circuit 

 perfectly straight, and also over the same circuit passed about 

 pins so as to make sharp angles: — the result of the charge on 

 fusing a given length of wire was not influenced, which could 

 hardly have been if the angular portions had thrown off" or 

 discharged into the neighbouring pins, &c. any of the charge, 

 it being well known that the least diminution of (juantity is 

 fatal to a delicate experiment on the fusion of wire. 



{v). Discharge a given quantity of electricity by a continu- 

 ous rod free of edges, through a wire passed through the ball 



Mahon's. The latter relates to the influence of a permanently charged 

 conductor on a body neutral ; whereas Priestley's applies to the action of 

 wires carrying vanishing quantities of electricity, the very essence of Mr. 

 Sturgeon's experiment. Dr. Priestley would not have told us, had he 

 brought his rod near the free side of his battery, that then the pith balls 

 were not moved. 



