Mr. C. Tomlinson's Experiments on the Electrical Fly, 203 



trary way. This experiment was contrived in order to try 

 whether the electric fluid, which issues so freely from pointed 

 bodies, would have any effect to move these bodies by its reac- 

 tion j and that it has such an effect seems sufficiently manifest 

 from the event. Mr. Hamilton apprehends that the electric 

 particles, by their elastic force, issue directly forwards from the 

 points, and endeavour to expand themselves, but meeting with 

 some resistance from the air, force the wire to move backwards 

 in a contrary direction — much in the same manner that a Catha- 

 rine wheel is made to turn round in a direction contrary to that 

 in which the small rockets attached to the periphery discharge 

 themselves." 



Soou after this experiment was made known, Mr. Kinnersley* 

 repeated it with negative electricity, " expecting the needle to 

 turn the contrary way, but was extremely disappointed, for it 

 still went the same way as before." He then endeavours to 

 account for the fact in the following manner. He says, " When 

 the stand was electrified -f , I suppose that the natural quan- 

 tity of electricity in the air being increased on one side by what 

 issued from the points, the needle was attracted by the lesser 

 quantity on the other side. When electrified negatively, I 

 suppose that the natural quantity of electricity in the air was 

 diminished near the points ; in consequence whereof the equili- 

 brium being destroyed, the needle was attracted by the greater 

 quantity on the opposite side." 



Kinnersley attempts to justify this view by the following 

 observations : — " The doctrine of repulsion in electrized bodies 

 I begin to be somewhat doubtful of. I think all the pheno- 

 mena on which it is founded may be well enough accounted for 

 without it. Will not cork balls electrized negatively separate 

 as far as when electrized positively ? And may not their sepa- 

 ration in both cases be accounted for upon the same principle, 

 namely, the mutual attraction of the natural quantity in the air, 

 and that which is denser or rarer in the cork ball V 



Dr. Priestley, commenting on these experiments, remarked 

 that the pointed wire turning the same way, whether electrified 

 plus or minus, may by some be taken as a proof " that the elec- 

 tric fluid issues out at the points in both cases alike, and by the 

 reaction of the air is together with the points driven backwards — 

 contrary to what ought to have been the case if the electric fluid 

 had really issued out of the points in the one case and entered 

 in the other"t- 



* Phil. Trans. 1762, p. 86, " New Experiments in Electricity, in a letter 

 from Mr. Ebenezer Kinnersley to Benjamin Franklin, LL.D., F.R.S." The 

 letter is dated "Philadelphia, March 12, 1761." 



t History of Electricity, 4th ed. (1775) p. 395. 



