VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 459 



extremity, and a copper ball, 5 inches in diameter, screwed on to the lower end, 

 formed one of the parts. This part was supported by a stand of wood having a 

 cap of brass at the top, into which the brass rod was occasionally screwed. The 

 other part of the circuit consisted of a brass rod also, one end of which branched 

 out in the form of a fork with two prongs, that pointed towards the centre of 

 the copper ball ; and those prongs were so constructed, that either of them 

 could be made longer or shorter, just as the experiment required. On the end 

 of one of the prongs was fixed a ball of brass, -|- of an inch in diameter, and on 

 the other a sharp steel point or needle. The shoulder of this fork screwed into 

 a small plate of iron fixed on the inside of a wooden vessel, containing the 

 greatest part of a cylindrical glass jar 12 inches and f high, and about 4 inches 

 in diameter. The coating of this glass (which was tin-foil) measured nearly 144 

 square inches on each surface. Besides this coating, part of the inside of the 

 wooden vessel was coated also with tin-toil, for the purpose of making a secure 

 communication between the iron plate and the outer coating of the jar. Within 

 the jar itself was fitted a cylinder of wood, covered with tin-foil also, to make a 

 communication between the inside coating of the glass and a brass rod fixed 

 upright in the centre of the wooden cylinder. This upright rod having a ball of 

 brass at the end, 4 of an inch in diameter, was bent towards the first part of the 

 circuit: so that the two balls being on a level, looked towards each other, but were 

 placed from time to time at difi'erent distances, as occasion required, and thus 

 answered the purpose of an electrometer. 



The results of the several experiments, made by Dr. Lind, Mr. Cavallo, and 

 Mr. Wilson, show, that in 23 experiments there was not any one instance 

 where the ball was struck at a greater distance than the point, nor even at the 

 same distance. It is remarkable, that in 2 or 3 experiments where the point was 

 farther off than the ball, both the point and the ball were struck at the same 

 time; which shows, that the influence of the point, though placed at a greater 

 distance, was equal to the influence of the spherical termination placed con- 

 siderably nearer. 



On an application to Dr. Higgins, he favoured them with the use of his 

 machine; the cylinder of which, when excited with the assistance of his amal- 

 gama, acted so powerfully, that it charged the jar, accompanying the new 

 instrument, very readily. They began the experiments, where the electrometer 

 was struck at the greatest distance, and then adjusted the distances of the ball 

 and point from the copper ball accordingly; so that if the point was struck 

 (when they were adjusted) the moving of the ball -^V part of an inch would occasion 

 the ball to be struck in preference to the point, and vice versa. Afterwards 

 they lessened the striking distance of the electrometer in every experiment till 

 they attained the least distance. On reversing part of the apparatus, all those 



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