COMPARATIVE POWERS OF ELECTRICAL MACHINES. £]Q 



pulley, the proportionate diameter of which are as four to 

 o^),und a single plat* machine oi' 24 inches diameter, 

 turned by a single winch, as usual. The management and 

 excitation of each machine were undertaken by the indivi- 

 dual who had constructed it, and an equal advantage was 

 ithus afforded to both. To ensure greater accuracy, the 

 results noted were in all cases the mean result of repeated 

 experiments; without this precaution, the sources of ano- 

 maly would be much more frequent and numerous. 



jYfr. Cuthbertson's experiments (published in this jour- Best test of 

 nal, 4to edition, vol. II, pave 525 : and in his Essay onprac- « lectri c a lacj 

 tical Electricity and Galvanism, parts 6 and 7)- have deci- 

 sively proved, that no known test of electrical action is so 

 uniformly accurate, as that of the gradual increase of 

 charge, conveyed to a known measure of coated surface, 

 measured by his electrometer, and by the fusion of deter- 

 minate quantities of wire. These were consequently the 

 means most frequently employed, and on which the great- 

 est reliance was placed; but in the progress of inquiry B ut everT 



recourse was also had to every known means of measuring known raeana 



.-.- here era- 



Comparative quantities. ployed. 



In our first experiments much difficulty was experienced, Difficultksat 

 in consequence of the variation produced in charges of high first experi- 

 jnteusity, by the di.Terent arrangement of the conductors, mounted. 

 (a circumstance which cannot be avoided in the present 

 form of the instruments): but by altering the size and The two ma- 

 situation of the terminating balls, and modifying the charge, power °* ** 

 the production of tolerably uniform results was at length 

 accomplished. The mean result of nearly one hundred 

 distinct trials tended to prove, that the charging power of 

 the two instruments was precisely equal ; and this conclu- 

 sion was rendered indisputably accurate by the following 

 experiments. 



Exp. 1, A battery of 15 jars, exposing about 17 square proved by ex* 

 feet of coated surface, was connected with Mr. Cuthbert- P eriments * 

 son's electrometer, the slider on the arm placed at 15 

 grains. 4 feet of Iron wire, T i G of an inch diameter, were 

 placed in the circuit. The battery was fivft charged by 

 the cylinder, liiu turns of the wheel effected the dis- 

 charge, the wire was rendered red hot and fused into balls. 



