PHYSICS, EIGHTEENTH CENT. ELECTRICITY. 327 



the ground, or, as the phrase goes in electrical matters, " insulating''' 

 himself, Franklin excited his glass tube by rubbing it with his hand, 

 and then drew off its electricity into his own body. It was then well 

 known that, if under these circumstances he had drawn off the elec- 

 tricity from an excited tube presented by another person, he would 

 have been electrified ; but Franklin found that in his experiment his 

 body showed no signs whatever of electrification. Now, he reasoned, 

 the circumstance of having rubbed the tube had effected precisely such 

 a change in him, that the electricity he afterwards drew from the tube 

 failed to produce any effect whatever, or, in other words, its operation 

 was exactly neutralized by the state induced by the rubbing. He 

 tested these views by separately insulating two persons, one of whom 

 rubbed the tube, and the other drew electricity from it. In this case 

 both became electrical, exhibiting the usual signs, such as attractions 

 of light bodies and sparks. But when these persons, still insulated and 

 electrified, touched each other, all signs of electricity vanished ; and 

 it was noticed that in touching, the spark produced was brighter than 

 if they had touched a third person. Upon such facts as these the main 

 features of the Franklinian theory were founded. Franklin considered 

 that every body in nature contained in its ordinary state some definite 

 quantity of a subtle fluid which constitutes electricity. In this condi- 

 tion, all bodies being equally supplied with the fluid, no signs of its 

 existence are manifested. But when a glass tube is rubbed, the ordi- 

 nary or natural distribution of the fluid is disturbed, the glass receives 

 more than its natural share, and the excess is derived from the hand 

 that rubs the tube. Thus, from the body of the operator electricity 

 is drawn off on the glass tube ; but if he simply stands on the ground, 

 the deficiency is immediately supplied from the earth, and he mani- 

 fests no electrical signs whatever. If he is insulated he does be- 

 come electrified, provided he does not allow the electricity accumu- 

 lated in the tube to pass back again into his body, thus restoring to 

 him his normal quantity of the fluid. Franklin introduced the terms 

 positive and negative electrification, to express the respective condi- 

 tions of bodies containing more or less than their normal amount of 

 electric fluid. Thus, as we have seen, he regards an excited glass 

 tube as positively electrified, while the hand which rubs it becomes 

 negatively electrified. Similarly he recognizes negative electrification 

 in a piece of rubbed sealing-wax. It will be observed that Franklin 

 accounts for the facts of two different electrical conditions by the hy- 

 pothesis of a single fluid in excess or defect, while Du Fay's theory 

 (page 320) requires two different fluids to explain the phenomena. 

 Franklin's theory appeared at first to have the advantage on the score 

 of simplicity. But some difficulties were afterwards observed. It was 

 a necessary part of Franklin's theory that the particles of the electric 

 fluid repel each other.' but attract the particles of matter ; and he ex- 

 plains the movement of electrified bodies by this reciprocal attraction. 



