184: On Franklin's Theory of Electricity, [March, 



was published in the Philosophical Transactions so long since as 

 the year 1789. 



" The escape,*' says Mr. Nicholson, in a paper detailing some 

 experiments with a powerful machine, *' of negative electricity 

 from a ball, is attended with the appearance of straight sharp 

 sparks with a hoarse or chirping noise. When the ball was less 

 than two inches in diameter it was usually covered with short 

 (lames of this kind, which were very numerous. 



" When two equal balls were presented to each other, and 

 one of them was rendered strongly positive, while the other 

 remained in connexion with the earth, the positive brush or 

 ramified spark was seen to pass from the electrified ball : when 

 the other ball was electrified negatively, and the ball, which 

 before had been positive, was connected with the ground, the 

 electricity exhibited the negative flame, or dense, straight, and 

 more luminous spark, from the negative ball ; and when the one 

 ball was electrified plus and the other minus, the signs of both 

 electricities appeared. If the interval was not too great, the 

 long zigzag spark of the plus ball struck to the straight flame of 

 the minus ball, usually at the distance of about one-third of the 

 length of the latter from its point, rendering the other two-thirds 

 very bright. Sometimes, however, the positive spark struck the 

 ball at a distance from the negative flame. These effects are 

 represented in Plate V. figs. 1, 2, and 3. 



Two conductors of three-quarters of an inch diameter, with 

 spherical ends of the same diameter, were laid parallel to each 

 other, at the distance of about two inches, in such a manner as 

 that the ends pointed in opposite directions, and were six or 

 eight inches asunder. These, which may be distinguished by 

 the letters P and M, were successively electrified as the balls 

 were in the last paragraph. When one conductor P was posi- 

 tive, fig. 5, it exhibited the spark of that electricity at its extre- 

 mity, and struck the side of the other conductor M. When the 

 last-mentioned conductor M was electrified negatively, fig. 4, 

 the former being in its turn connected with the earth, the sparks 

 ceased to strike as before, and the extremity of the electrified 

 conductor M exhibited negative signs, and struck the side of 

 the other conductor. And when one conductor was electrified 

 plus and the other minus, fig. 6, both signs appeared at the same 

 time, and continual streams of electricity passed between the 

 extremities of each conductor to the side of the other conductor 

 opposed to it." '' The effect of a positive surface appears to 

 extend further than that of a negative." 



This experiment will Meed few comments, for it is sufficiently 

 evident that if the form of a spark or its direction, is to deter- 

 mine the existence of an electric fluid, this experiment proves 

 that there are two. Nor is it easy for an unprejudiced observer 



• Phil. Trani. vol. Ixxix. pp. 978—280. 



