448 Mi\ M. Donovan on the supposed Identity of the Agent 



The trifling nature of the spark is shown strikingly by Mr. 

 Gassiot's experiments : with a nine-gallon Leyden battery, 

 charged by 1024 pairs of plates, that gentleman could only pro- 

 ject a spark to a distance of j—j^dth of an inch. 



In support of the inference here drawn of the very trifling 

 nature of the shock, and the inconsiderable quantity of electri- 

 city which a Leyden battery is capable of communicating, when 

 charged by a voltaic series, I shall detail an experiment lately 

 made in the laboratory of the Royal Dublin Society, by Professor 

 E. Davy and me. We used twenty Wedgwood-ware troughs, 

 each containing ten cells ; the number of plates was therefore 

 200 of zinc and the same of copper, each plate presenting a sur- 

 face of 20 square inches on each side. The exciting liquid in 

 each trough consisted of 140 ounces of water, 3| ounces of con- 

 centrated sulphuric acid, If ounce of nitric acid, and the same 

 of muriatic acid, all taken by measure. When the battery was 

 connected and put in action, the polar wires, armed with charcoal 

 terminations, were brought in contact. An instantaneous burst 

 of light, of dazzling splendour, announced that the battery was 

 in high action. Having removed the charcoal terminations, we 

 connected the polar wires with the inside and outside coatings 

 of a Leyden battery of six jars, the total coated surface of which 

 amounted to 12^ square feet, and after two or three moments of 

 contact, applied a discharging rod; but there was not the 

 slightest spark ; nor were several repetitions of the experiment 

 attended by any better success. Having established the con- 

 nexions as before, we tried to obtain a shock from the Leyden 

 battery when it was detached, but neither of us experienced the 

 slightest sensation after several trials. 



We then proved that there was no defect in the Leyden bat- 

 tery, and that it was adequate to receive and retain the smallest 

 charge, had there been any, by connecting it with a Nairne's 

 electrical machine. It resulted that three turns of its cylinder 

 were sometimes sufficient to afford a spark visible in day-light, 

 from the Leyden battery ; and that six turns were adequate to 

 the communication of a very slight shock. This cylinder is 6 : | 

 inches in diameter, the rubber is 8 inches in length ; the con- 

 ductors ai*e each 3 inches in diameter and 12 inches in length. 

 Thus it is a very small machine ; its sparks vary from an inch to 

 an inch and a quarter in length, are very dilute in appearance, 

 and their snap feeble. 



The experiment proved that three turns of this cylinder af- 

 forded from the Leyden battery a perceptible spark ; hence 

 whatever electricity the 200 pairs of plates had communicated 

 to it must have been less, as it was altogether undiscoverable. 

 A subsequent trial of the cylinder, made immediately after the 

 experiments with the Leyden battery, proved that each revolu- 



