338 Mr. Latimer Clark [March 15, 



tricity passing. Their greater energy when the tension was increased, 

 was an indirect effect, due not to that tension, but to the increased 

 quantity which passed in a given time by reason of the increased 

 tension. A galvanometer wound with a few turns of thick wire was 

 shown to be deflected as powerfully by one cell as by six, or even by 

 600 cells of the same size, because by reason of its shortness the wire 

 conveyed freely the whole quantity which one cell could produce, which 

 was the same as that produced by the whole 600 ; but any alteration 

 in the size of the cell produced a consequent change in the quantity 

 and in the deflection of the galvanometer. On the other hand, a 

 galvanometer with many thousand turns of fine wire gave the same 

 deflection with a battery formed of a small gun-cap, as with one of 

 twenty square feet of surface, because the quantity in this case was 

 regulated and limited not by the size of the plates, but by the power 

 of conduction of the wire ; the quantity being therefore the same in 

 both cases. In every case the deflection was dependent solely on the 

 quantity of electricity actually passing through the instrument with- 

 out reference to its tension. 



The combustion of metals was shown to be a phenomenon depen- 

 dent on quantity, and not on tension ; one cell of Grove's battery 

 ignited a certain length of platina wire ; and whatever its size it would 

 ignite no greater length ; but two, three, or more cells were shown to 

 ignite two and three times the original length, the quantity passing in 

 the greater length being under the higher tension, precisely the same 

 as in the original length. This explained Faraday's oft misunderstood 

 remark, that the same quantity of electricity which would ignite an 

 inch of wire, would ignite a foot or a mile. 



The pain and shock experienced on touching a powerful battery, or 

 shocking coil, or Leyden jar, were proportionate to the quantity of 

 electricity passing through the system, and not to the tension. A 

 carrier ball or minute Leyden jar charged to the highest tension, would 

 produce no sensation if the quantity were absent, and the same was 

 the case with a Zamboni's pile. Sparks nearly eighteen inches long 

 were received from an electrical machine ; but although of this high 

 tension, they produced no violent physiological effects, owing to their 

 deficiency in quantity. Long sparks, nevertheless, produced greater 

 effects than short ones, because at double the striking distance the 

 tension is doubled, and the quantity is therefore twice as great. The 

 quantity contained in a Leyden jar or battery is comparatively great, and 

 the effect on the system proportionately violent. Two conditions were 

 necessary for these effects : first, that the quantity present should be 

 considerable ; and secondly, that the tension should be sufficiently 

 great to make it pass through the system. A battery of two or three 

 cells, which could readily fuse platina wire, was shown to produce no 

 painful sensation on the tongue, because, although the quantity was 

 abundant, the tension was low ; while another battery of 600 cells, 

 which produced the most intolerable shock to the system, had, from 

 its deficiency in quantity, scarcely any power to fuse wire. The 



