Royal Institution. 319 



heat varies with reference to the pressure, and is still believed to be 

 engaged in researches on the subject, one involving questions of 

 •which experiments on the mechanical effects of elastic fluids seem 

 to offer the most promising means of solution. 



One of the greatest difficulties which had presented itself to 

 Mr. Grove's mind, with reference to the theory of Carnot, had 

 been one of analogy, derived from the received theories of elec- 

 tricity. Many electrical cases might be cited in which no electricity 

 is supposed to be lost, though a certain mechanical effort is produced 

 by the electricity ; if, for instance, a ball vibrates between a posi- 

 tively and a negatively electrified substance, none of our electrical 

 theories lead us to believe that any difference in the actual amount 

 of electricity transferred would be occasioned by the ball being 

 attached to a lever which would strike a wheel or produce any other 

 mechanical effect. 



In preparing this evening's communication an experiment had 

 occurred to him, which, though performed with imperfect apparatus 

 Eind therefore requiring verification, does, as far as it goes, support 

 the view derived from the negation of perpetual motion, viz. that 

 when electricity performs any mechanical work which does not 

 return to the machine, electrical power is lost. The experiment is 

 made in the follow-ing manner. A Leyden jar of one square foot 

 coated surface has its interior connected with a Cuthbertson's elec- 

 trometer, between which and the outer coating of the jar are a pair 

 of discharging balls fixed at a certain distance (about half an inch 

 apart). Between the Leyden jar and the prime conductor is in- 

 serted a small unit-jar of nine square inches surface, the knobs of 

 which are 02 inch apart. 



The balance of the electrometer is now fixed by a stiff wire 

 inserted between the attracting knobs, and the Leyden jar charged 

 by discharges from the unit-jar. After a certain number of these 

 (twenty-two in the experiment performed in the theatre on this 

 occasion), the discharge of the large jar takes place across the 

 half-inch interval ; this may be viewed as the expression of elec- 

 trical power received from the unit-jar. The experiment is now 

 repeated, the wire between the balls having been removed, and 

 therefore the ' tip ' or the raising of the weight is performed by the 

 electrical repulsion and attraction of two pairs of balls ; at twenty- 

 two discharges of the unit-jar the balance is subverted, and one knob 

 drops upon the other, but no discharge takes place, showing that some 

 electricity has been lost, or converted into the mechanical power 

 which raises the balance. By another mode of expression the electricity 

 may be supposed to be masked or analogous to latent heat, and 

 would be restored if the ball were brought back, without discharge, 

 by extraneous force. 



This experiment has succeeded in so large an average of cases, 

 and so responds to theory, that, notwithstanding the imperfection of 

 the apparatus, Mr. Grove places much reliance on it ; indeed, it is 

 difficult to see, if the discharges or other electrical effects were the 

 same in both cases, why the raising the ball, being extra and the ball 



