Mr. C. Tomlinson's Experiments on the Electrical Fly, 211 



If brought near the knob of a charged jar, the points are first 

 attracted and then repelled, after which the fly rotates briskly, 

 and continues to do so until the charge is nearly drawn off. The 

 experiment succeeds equally well whether the jar be charged 

 vitreously or resinously. 



The fly was placed within a cylindrical spangled Leyden jar, 

 10 inches high and 4J inches in diameter; the tinfoil coatings 

 rose to the height of 8£ inches ; a chain from the prime con- 

 ductor trailed down the inside of the jar. The fly was arranged 

 so as to be on a level with the top of the coatings. Soon after 

 the electrical machine was set in action the fly began to rotate 

 and dissipated the charge, so that it was impossible to overcharge 

 or even to fully charge the jar. When the electrical machine was 

 stopped, the fly continued to move until only a weak charge was 

 left in the jar. 



A second fly poised on a point in the hand was set spinning 

 when held in the powerful electrical aura which diverged from 

 the mouth of the jar, and which could thus be traced to a great 

 distance. The aura was sufficiently powerful to give motion to a 

 heavy fly 6 inches in diameter and weighing 123 grains, so long 

 as it was uninsulated ; but directly it was insulated it ceased to 

 move, for the reason already given. 



The fly was lowered in the spangled Leyden jar so as to be 

 about an inch below the top edge of the coatings. On charging 

 the jar, the fly did not rotate until induction was assisted by 

 holding a finger just over the jar. On raising the fly so as to 

 be on a level with the mouth of the jar, or even higher, motion 

 became much more sensitive, on account of the facility with which 

 the polarized particles of air could discharge on its points. 



When the fly was placed on a point within an insulated copper 

 saucer, 5 inches in diameter and 1J inch deep in the middle, 

 and the electricity sent in by a chain attached to the lower end 

 of the point, there was no motion whatever, even though the 

 finger or a metal point were held over the fly, the whole of the 

 electricity passing to the outside of the copper dish. 



4. The Fly in rarefied air. 



A small air-pump was insulated and the fly placed on its table 

 and covered with a bell-glass receiver. The air was exhausted 

 to 1 inch of the gauge, and the apparatus electrified ; no 

 motion whatever could be produced in the fly either by present- 

 ing the finger or a metal point to the receiver, or by occasionally 



hanging it up by the other. In either case the needle is alternately 

 attracted and repelled if brought within a few inches of the knob of a 

 charged jar. 



P2 



