ELECTRICITY. 91 



as the expression of electrical power received from the unit 

 jar. The experiment is now repeated, the wire between the 

 knobs having been removed, and therefore the ' tip/ or the 

 raising of the weight, is performed by the electrical repulsion 

 and attraction of the two pairs of balls. At twenty discharges 

 of the unit jar the balance is subverted, and one attracting 

 knob drops upon the other ; but no discharge takes- place, 

 showing that some electricity has been lost or converted into 

 the mechanical power which raised the balance. 



By another mode of expression the electricity may be sup- 

 posed to be masked or analogous to latent heat, and it would 

 be restored if the ball were brought back without discharge by 

 extraneous force. If the discharge or other electrical effects 

 were the same in both cases, then, since the raising of the 

 ball or weight is an extra mechanical effort, and since the 

 weight is capable by its fall of producing electricity, heat, 

 or other force, it would seem that force could be got out of 

 nothing, or perpetual motion obtained. 



The above experiment is suggestive of others of a similar 

 character, which may be indefinitely varied. Thus I have 

 found that two balls made to diverge by electricity do not 

 give to an electrometer the same amount of electricity as 

 they do if, whilst similarly electrified, they are kept forcibly 

 together. This experiment is the converse of the former one. 

 There is an advantage in electrical experiments of this class 

 as compared with those on heat, viz. that though there is no 

 perfect insulation for electricity, yet our means of insulating 

 it are immeasurably superior to any attainable for heat. 



Electricity directly produces heat, as shown in the ignited 

 wire, the electric spark, and the voltaic arc ; in the latter, the 

 most intense heat with which we are acquainted so intense, 

 indeed, that it cannot be measured as every sort of matter 

 is dissipated by it. 



In the phenomenon of electrical ignition, as shown by a 

 heated conjunctive wire, the relation of force and resistance, 

 and the correlative character of the two forces, electricity and 

 heat, are strikingly demonstrated. Let a thin wire of platinum 

 join the terminals of a voltaic battery of suitable power, the wire 

 will be ignited, and a certain amount of chemical action will 



