844 Examination of the eleSiric Capacity of Folia's Pile. 



the fpark *. But it is the charafter of ele£tric (hocks which arc felt to equal diftancet 

 from the extremities of the animal, that thofe which are produced by a fmall quantity of 

 eleftricity at a high intenfity, produce a fudden and more tranfient fenfation than thofe 

 which are produced by a large quantity of ek£lricity at a low intenfity, and, therefore, 

 probably moving more flowly. 



From this laft circumftanec I found it very difficult to take a fhock from one fquarc . 

 foot of coated glafs which fiiould much refemble the galvanic fhock. Whira the jar wag 

 charged to give an explofive fpark of one-twentieth of an inch, the fliock extended above 

 the elbows not quite fo far as that from a pile of lOO half crowns ; but the pain was much 

 more fudden, fharp and tranfient. The denfe galvanic (hock feemed to (ill the limbs 

 producing univerfal perfpiration, and leaving a difpofition to tremor and unfteadinefs in 

 the parts through which it had pafTed. When the explofion of the jar meafured only 

 one-fortieth of an inch, the (hock ftill proved to be more unpleafant at the inflant than that 

 of any of the piles I have tried, though it did not extend quite to the elbows, and may be 

 confidered as equal in this refpedt to the fet of which the eleftricity was tried by the con- 

 denfer, as dcfcribed at page 184 of our prefent volume. I (hall, therefore, take this as 

 one term of comparifon. Another experiment was wanting to determine the length of 

 the fpark anfwering to the intenfity at which the gold leaf of Bennet's electrometer ftrikea 

 Its coatings. For this purpofe I took two equal ele£lrical jars, and charged one of them, 

 fo as to give an explofive fpark one-thirtieth of an inch in length. In this (ituation the 

 charged jar was made to communicate with the other in the fame manner as jars in a bat- 

 tery at top and bottom. It was then removed i having, in faft, loft half its charge. 

 The receiving jar was in the next place difcharged, and a connexion again made as before* 

 This fecond procefs reduced the original charge to one-fourth. A third reiteration re* 

 duced it to one-eighth ; and it may eafily be conceived that by continuing the geometrical 

 feries, it was in my power to reduce my charge very much indeed. After feven touches 

 the jar ftill caufed the leaves to diverge nearly to their greateft extent-, and in fome 

 repetitions of the experiment the leaves ftruck. The eleflricity in- this cafe was reduced 

 to fig part, and, confequently, would have afforded a fpark of -j-^ of -j-'^, or about y-^^ 

 of an inch f . We may, therefore, take it as a rule, that Bennet's electrometer, at the 

 higheft ftate of ele£lricity, had this intenfity. 



But we are to compare this intenfity with another ftill lower. The filk face of the con- 

 denfer, ufed with the galvanic pile in the experiments referred to, is about one-fiftieth 

 of an inch thick, and the leaves ftruck when the plate was raifed about half an inch ; the 

 diftance being thus increafed twenty- five, times. The el'edlric intenfity, or explofive fpark 



* The Hon. Hen. Cavendifli, Efq. found that four jars of the fame fize andthicJcnefs gave nearly the 

 fame, or rather a greater, fhock than one of them charged with half the quantity of eleftricity. Philofl 

 Tranf. LXVI. 196. 



f The length of the fpark being as the quantity of elefliicity cettrls paribus in moderate intenfities, 



of 



