90 CORRELATION OF PHYSICAL FOKCES. 



the former is of much greater intensity than the latter, or has a 

 greater power of overcoming resistance, but acts upon a much 

 smaller quantity of matter. If, then, a voltaic battery be 

 formed with a view to increase the intensity and lessen the 

 quantity, the character of the electrical phenomena approxi 

 mate those of the electrical machine. In order to effect this, 

 the sizes of the plates of the battery and thence the quantity 

 of matter acted on in each cell, -must be reduced, but the 

 number of reduplications increased. Thus if in abattery of 100 

 pairs of plates each plate be divided, and the battery be arranged 

 so as to form 200 pairs, each being half the original size, the 

 quantitative effects are diminished, and the effects of intensi 

 ty increased. By carrying on this sub-division, diminishing 

 the sizes and increasing the number, as is the case in the vol 

 taic piles of Deluc and Zamboni, effects are ultimately pro 

 duced similar to those of Franklinic electricity, and we thus 

 gradually pass from the voltaic arc to the spark or electric 

 discharge. 



This discharge, as I have already stated, has a colour de 

 pending in part upon the nature of the terminals employed. 

 If these terminals be highly polished, a spot will be observed, 

 even in the case of a small electric spark, at the points from 

 which the discharge emanates. The matter of the terminals 

 is itself affected ; and a transmission of this matter across 

 the intervening space is detected by the deposition of minute 

 quantities of the metal or substance composing the one, upon the 

 other terminal. 



If the gas or elastic medium between the terminals be 

 changed, a change takes place in the length or colour of the 

 discharge, showing an affection of the intervening matter. 

 If the gas be rarefied, the discharge gradually changes with 

 the degree of rarefaction, from a spark to a luminous glow or 

 diffuse light, differing in colour in different gases, and capable 

 of extending to a much greater distance than when it takes 

 place in air of the ordinary density. Thus, in highly attenu- 



