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LXXIII. On the FranKlinian Theory of the Leyden Jar ; "with 

 Remarks on Mr. Donovan's Experiments. By Mr. Thomas 



HOWLDY. 



To Mr. Tilloch. 



Sir, — 1 HAVE sent you for insertion in the next number of your 

 Magazine, a demonstration of some principles of the Franklinian 

 theory of the Leyden jar ; with an exposition of the fallacious 

 experiments which Mr. Donovan has opposed to them in his 

 *' Reflections on the Inadequacy of the principal Hypotheses to 

 account for the Phaenomena of Electricity." 



The following extract from the *« Reflections" contains an 

 account of two experiments made by Mr. Donovan, the results 

 of which he considers as opposing Franklin's doctrine of accu- 

 mulation and deficiency. " During the process of charging, 

 both surfaces (of a jar) ought to manifest their characteristic 

 properties in proportion as the charging increases. Whether or 

 not this is the case, will be seen by the following experiments. 

 The apparatus employed was an insulated jar, from the stem of 

 which projected a wire at right angles, and from the outside 

 coating another, two pith-balls being attached to each by means 

 of gilt thread. The jar, perfectly dry, is to be placed on the 

 insulating stand, and a chain is to be coimected with the out- 

 side, so as to form a communication with the ground. The 

 electric machine being in strong action, is made to pour in a- 

 stream of sparks until the jar be fully charged. The chain be- 

 ing removed, the balls connected with the inner surface will be 

 repelled by excited sulphur, and those with the outer surface 

 will be attracted. If the inside be now positi\e, — why are the 

 balls repelled by sulphur ? And if the outer surface be negative, — 

 why are its balls attracted ? If the jar be weakly charged, the 

 results are as described by Franklin; and it was no doubt on such 

 that this philosopher made his observations. But were the 

 doctrine of accumulation and deficiency well founded, the re- 

 sults should be the more decided as the jar is more strongly 

 charged. Yet when the hypothesis supposes the jar to contain 

 the greatest quantity of electricity, it is then that it evinces 

 symptoms of containing the least." — -Phil. Magagine, vol. xHv. 

 p.lUl. 



The apparently contradictory results of the above-described 

 experiments very much excited my attention on perusing Mr. 

 Donovan's " Reflections ;" and I strongly suspected that he had 

 been deceived by mere ap])earances. 



In consequence of this suspicion, I determined to investigate 

 Vol. 46. No. 212. Dec, 1815. C c the 



