468 



Davj' charged a Leyden battery with 2000 pairs of zinc and 

 copper plates, each plate exposing thirty-two superficial inches 

 of metal to the exciting liquid ; the total surface being 128,000 

 square inches. On making the proper connexions, with the 

 Leyden battery, " either a shock or a spark could be per- 

 ceived." Thus the shock was barely perceptible ; and to this 

 Mr. Donovan added his own testimony of the shock from a 

 Leyden battery, charged by 1000 pairs of plates, which he re- 

 presented as exceedingly feeble. 



In support of the inference drawn of the trifling nature of 

 the shock, and the inconsiderablequantity of electricity which 

 a Leyden battery is capable of communicating, when charged 

 by a voltaic series, Mr. Donovan detailed an experiment made 

 by Professor E. Davy and himself, in which twenty Wedg- 

 wood ware troughs, each containing ten cells, were employed, 

 with a total number of 200 pairs of plates excited by dilute 

 acids. When charcoal points, fixed to the polar wires, were 

 brought into contact, an instantaneous burst of light, of 

 dazzling splendour, announced that the series was in high ac- 

 tion. On attempting to charge a Leyden battery of twelve or 

 thirteen square feet of coated surface with this voltaic series, 

 neither shock nor spark could be obtained. Yet it was proved 

 that the charge communicated to the Leyden battery by three 

 turns of a very small electric machine was sufficient to enable 

 the battery to give a spark visible in day-light, the three turns 

 producing three weak sparks of one inch in length. Six turns 

 of the cylinder, that is six one-inch sparks, enabled the Ley- 

 den battery to give a sensible shock. This failure was sup- 

 posed to be explicable by the small size of the Leyden battery 

 compared with that of Van Marum, the ratio being as \2\ to 



So far as all the experiments, whether these last, or those 

 of Van Marum or Davy, are concerned, there seems to be no 

 evidence of great quantity of electricity in the voltaic series. 

 But, even if there were, it was stated that none of the fore- 



