concerned in the Phenomena of ordinary Electricity, fyc. 4A7 



tion of Van Marurn's machine to occupy half the time, the 

 quantity thrown in during the six contacts would amount to a 

 single one-inch spark. Indeed the divergence of the gold-leaf 

 electrometer, connected with the Leyden battery, seems to have 

 indicated a very low intensity, since it amounted to no more than 

 five-eighths of an inch, an effect which would be doubled by the 

 approach of a bit of excited sealing-wax, without any battery. 

 It is quite plain therefore that the shock given by the Leyden 

 battery must have been a very small one. 



It is well known that the shock of the pile is remarkable for 

 extending its influence but a short way along the arms ; it affects 

 the fore-arm rather than the arm ; to convey it to the shoulder 

 a considerable number of pairs must be requisite ; and it is to be 

 recollected that the pile is the weakest in its effects of all the 

 forms of the voltaic battery. In Van Marurn's case the shock 

 was only equal to that of 100 pairs ; and if this was felt at the 

 shoulders, the fact only proves an uncommon degree of sensitive- 

 ness in the person. Perhaps when Van Marum stated that the 

 shocks " extended to the shoulders with much force," he only 

 meant " with much force making all due allowance for the weak- 

 ness of the pile itself ;" and in giving it this interpretation we 

 must recollect that the statement is made in a complimentary 

 letter from Van Marum to the illustrious inventor of the pile, 

 Volta himself. The meaning will plainly appear to be this 

 when his results are compared with those of Sir H. Davy, who 

 had at his disposal the most powerful apparatus that had ever 

 been constructed. Sir H. Davy's statement is on this account 

 the most valuable. He used the enormous power of 2000 pairs 

 of zinc and copper, each plate exposing 32 superficial inches of 

 metal to the exciting liquid; the total surface being 128-000 

 square inches. The shock from such a battery would be 

 dreadful, if not fatal : I can speak feelingly of the shock from 

 1000 pairs of new plates; anything more tremendous I could 

 not conceive ; it raised a large blister on one of the two parts 

 that received it, and almost prostrated me; what must double 

 the number be ? Yet, wonderful to say, a Leyden battery 

 charged by 2000 pairs gave a shock the force of which may be 

 inferred from Sir H. Davy's expression, that "on making the 

 proper connexion (with the hands), either a shock or a spark 

 could be perceived." Thus the shock was merely perceptible; 

 and this corresponds with my recollection of the shock from a 

 battery charged by 1000 pairs: Volta himself represents the 

 shock as sensible. It appears also that the spark was such that 

 it could be merely "perceived." It should be observed here 

 that any longer connexion than a momentary one, between the 

 Leyden battery and I he voltaic series, does not increase the 

 charge of the former. 



