ELECTRICITY. 77 



of cells to 400 or 500, the discharge will pass from one ter- 

 minal to the other before they are brought into contact. 

 The difference between what is called franklinic electricity, 

 or that produced by an ordinary electrical machine, and 

 voltaic electricity, or that produced by the ordinary voltaic 

 battery, is that the former is of much greater intensity than 

 the latter, or has a greater power of overcoming resistance ; 

 but, assuming an equal initial power, it 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- 

 mates 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 a battery 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 

 intensity increased. By carrying on this sub-division, dimi- 

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

 the voltaic piles of Deluc and Zamboni, effects are ultimately 

 produced 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 

 depending 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 



