Dr. Hare's Electrical Machine, &fc. 275 



as to be set in one straight line, or in any angle with each other. 

 0« one of the plates near the extremity not secured by the bolt, a 

 brass socket is soldered, into which a glass column C is cemented, 

 surmounted by a forceps. At the corresponding end of the other 

 plate, there is a brass rod R, perpendicular to the plate, and par- 

 allel to the glass column. This rod is also furnished with for- 

 ceps. Between these forceps, and those at F, supported and insu- 

 lated by the glass column C, a wire is stretched, which may be of 

 various lengths, according to the angle which the plates S S make 

 with each other. The pedestal should be metallic, or have a metallic 

 plate at bottom, in communication with the external coating of the 

 battery. This being accomplished, it is only necessary to charge 

 the battery, without subsequently breaking the communication be- 

 tween the inner coatings of the jars, and the prime conductor, by 

 which the charge is conveyed. In that case, touching the conductor, 

 is equivalent to a contact with the inner coatings of the jars, so far 

 as electrical results are concerned. Hence, by causing one of the 

 knobs of the discharger D, with glass handles, to be in contact with 

 the insulated forceps F, and then approximating the other knob to 

 the prime conductor B, the charge of the battery will pass through 

 the wire W, as it cannot descend by the glass column, nor reach the 

 operator through the glass handles. These should be longer than 

 represented in the cut. 



Long zigzag or erratic spark, contrasted with the short straight 



sparTc. 



" The cause of this difference between the lengths of the two electricities, we 

 have no means of explaining." — Thomson's work un Heat and Electricity. 



The object of the engraving on the following page is to represent 

 the different forms and lengths of the electric spark, which take 

 place between a large and a small ball, accordingly as they are made 

 negative or positive. The long and zigzag, or erratic spark A takes 

 place between a small ball attached to the positive pole, and a large 

 one associated with the negative pole. The short straight spark B 

 is elicited under circumstances the reverse of those just mentioned. 

 They are represented as simultaneous, but with the same machine, 

 can of course, only be obtained in succession. 



In no respect do the phenomena of mechanical electricity appear 

 more favorable to the Franklinian theory, and more inexplicable, 

 according to the doctrine of two fluids, than in the diversity of the 

 electrical spark in passing between a small and a large metallic ball, 



