Mr. C. Tomlmson's Experiments on the Electrical Fly. 215 



When the wires of the universal discharger were not more 

 than 2 inches apart in turpentine, the effects were very ener- 

 getic. A point held over the vessel at the distance of some feet 

 produced a regular upward rain of turpentine ; and even when 

 the machine was turned slowly, the turpentine played and 

 discharged upon the point as we must suppose air to do. A 

 knob held over the vessel produced a complete waterspout ; and 

 many seconds after the machine had ceased to be worked the tur- 

 pentine retained its charge, as was evident by the pit produced 

 in the liquid when a point was held over it at the distance of 

 some inches. 



6. Modification of the points. 



Seeing then that it is easy to make the fly rotate in liquid 

 dielectrics either with the points backwards as in air, or with the 

 points forwards, and not being able to trace any essential differ- 

 ence between air and a liquid dielectric except in density, I saw 

 no reason why the fly should not be made to rotate in air with 

 the points forwards. But this was no easy matter so long as the 

 points existed in their normal condition. By attaching little 

 discs of tinfoil to them by means of sealing-wax (fig. 7), the fly 

 rotated with the points forwards without any difficulty, or simply 

 by attaching knobs of sealing-wax to the points (fig. 8) they rotated 

 forwards * ; but what was very curious, if a candle were within 

 a foot or two of the fly with the wax knobs, it rotated backwards ; 

 or if, while rotating forwards, the flame of a spirit-lamp were 

 brought near, it soon came to rest and resumed its rotations 

 backwards. I next altered the fly so as to get rid of the bend 

 in the arm, and found that straight arms with discs of tinfoil at 

 the end rotated very well. Several forms of fly were constructed 

 on this pattern ; but the best form was a disc of tinfoil within a 

 key-ring attached to a knitting-needle 9 inches long passing 

 through a cap, and balanced with a brass knob at the other end, 

 as in fig. 9. One side of the disc was coated with sealing-wax, 

 and it rotated well with the metal side forwards ; and if set going 

 the other way, it soon pulled up and rotated with the metal side 

 forwards. 



These experiments seemed to favour Mr. Kinnersley's theory 

 of attraction, and I worked for some time in the direction pointed 

 out by it. The question was, at what part of the fly, on the 

 attraction theory, was the pull applied ? and, on this theory, what 

 was the influence of the point ? Could the point be got rid of in 

 any other way than by covering it with discs, or concealing it 

 with wax ? It could be bent inwards so as to form a loop 

 (fig. 10). This was accordingly done, and to make the direc- 



* I afterwards found pellets of bees' wax much more convenient. 



