COMPARATIVE POWERS OF ELECTRICAL MACHINE*. 3$! 



cord, instead of an insulating winch. I adopted this plan 

 to prevent the effect of that undulation, which has been 

 described by Mr. Nicholson as peculiar to cylinders (in , 

 consequence of their irregular surface, which occasions an 

 unequal pressure of the rubber) : and to obviate this in- 

 equality still more effectually, the rubber is so formed, that 

 the back of it acts as a horizontal spring; which keeps up 

 a steady, and nearly uniform pressure, without the imper- 

 fection of shortening the negative insulation. I have never 

 found this machine vary materially in its action, although I 

 frequently employ it through a whole course of lectures 

 without any fresh application of the amalgam; nor do I 

 find that its power of excitation is at all affected by a moist 

 atmosphere. 



Mr. Cuthbertson conjectured, that my machine owed Its power io- 

 tauch of its power to the multiplying wheels; and having ^*^ p1yi ]L 

 noticed, that the cylinder made four revolutions for one of wheels, 

 the wheel, requested me to try its action with a simple 

 winch. The pressure remaining the same as in the former 

 experiments, it required (as might have been expected) 

 four times the number of turns to produce any given effect. 

 The friction however was materially less, 2-|lbs. troy being These greatly 

 sufficient to move the handle from its horizontal position. increased the 



Soon after these experiments Mr. Cuthbertson informed . ' 



11111- i • -ii Applied to the 



me, that he had discovered an improvement in the plate p i a te machine, 



machine ; by which its charging power might be doubled, 

 trebled, or even quadrupled, without any inconvenience 

 but that of increased friction. I could not at first conceive 

 by what means this might be effected ; but after some 

 consideration concluded, it could only be accomplished by > 



the application of multiplying wheels to the plate machine; 

 and Mr. Cuthbertson then told me, this was the idea that 

 had occurred to him. 



It was agreed, that experiments in proof ©f Mr. C.'s in- Comparative 

 vention should be made at the conclusion of our compara- experiments, 

 tive experiments; and the requisite apparatus being com- 

 pleted, we resumed our inquiry. Before this second series 

 of comparative experiments, I made some alteration in the Rubber alter- 

 rubber of the cylinder, and furnished it with new silk ; sus- ed » &ne,r 3Lilc 

 pecting, that three years constaut wear might have so far api ' lC ' 



deranged 



