PHYSICAL SCIENCE. 



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spire in Philadelphia to execute his experiment, 

 when it occurred to him that by means of a boy's 

 liiite he could have a readier and better access to 

 I he region of thunder, than by any spire what- 

 ever. Preparing a large silk handkerchief and 

 two cross sticks of sufficient length on which to 

 extend it, he took the opportunity of the first ap- 

 proaching thunder-storm to take a walk into a 

 h'eld where there was a shade convenient for his 

 purpose. He confided his secret to nobody but 

 his son, who assisted him in raising the kite. 



After the kite was raised, a considerable time 

 elapsed before it exhibited any marks of being 

 electrified. One very promising cloud had passed 

 without effect ; when at length, just as he was 

 beginning to despair of his contrivance, the rain 

 having wetted the string, which was of hemp, and 

 rendered it a better conductor, he observed some 

 loose threads on it to stand erect and to avoid 

 one another, just as if they had been suspended 

 on a common conductor. Struck with this pro- 

 mising appearance, he presented his knuckle to 

 the key, which was tied to the end of the string, 

 and the discovery was complete he perceived a 

 very evident electric spark. Others succeeded 

 even before the string was fully wetted, so as to 

 put the matter past all dispute ; and when the 

 rain had wetted the string, he collected sparks in 

 abundance. This happened in June, 1752, about 

 a month after the French electricians had veri- 

 fied the theory, but before any information on 

 the subject had reached Dr Franklin. 



This experiment of Dr Franklin was attended 

 with extreme danger. Had his cord been more 

 moistened, or a better conductor than it was, it 

 is not unlikely that this celebrated man would 

 have fallen a victim to his temerity. This ac- 

 tually happened soon after to professor Richruann 

 of Petersburg, who was struck dead by a flash of 

 lightning on the 6th of August, 1753, drawn by 

 his apparatus into his room, as he was attending 

 to an experiment which he was making with il. 



3. The third discovery of Dr Franklin was the 

 analysis of the Leyden phial, which contributed 

 more than any thing else to establish his peculiar 

 theory of electricity. The Leyden phial in its 

 present state of simplicity was the work of Wat- 

 son and Nairn. It consists of a glass jar, of any 

 size, narrower at the mouth, and coated within 

 and without with tin foil to within two or three 

 inches of the mouth. The mouth has a piece of 

 dry varnished wood fitted into it; through which 

 there passes a wire having a knob on the top of 

 it, which rises a few inches above the mouth, and 

 which touches the tin foil coating at the bottom 

 of the jar in the inside. When the knob of this 

 jar is presented to the prime conductor of an 

 electrical machine, sparks pass into il, and for 

 every spark which passes into the inside of the 



jar, there may oe seen a corresponding spark 

 passing between the outside coating and a me 

 tallic knob held near it. The ins'ide of the jar 

 is charged with positive electricity, and the out- 

 side with negative electricity. Whenever the 

 inside and outside coating are brought into con- 

 tact, as by holding the jar in one hand and touch- 

 ing the knob with the other, the two electricities 

 rush into combination and an electric shock is felt. 



The Franklinian theory was exhibited in a 

 mathematical dress by jfEpinus in 1759, and by 

 Mr Cavendish in 1771. The theory proceeds on 

 the notion, that only one electrical fluid exists, 

 and that its particles repel each other, but are at- 

 tracted by matter. But several of the hypotheses 

 which they were obliged to assume are hardly 

 admissible. Thus they were obliged to admit 

 that matter repels matter, though of this repul- 

 sion no proof can be given. Neither are the phe- 

 nomena of electricity consistent with the notion, 

 that an affinity exists between matter and elec- 

 tricity. For it has been ascertained, that electri- 

 city is entirely confined to the surface of bodies, 

 and never penetrates into the interior; a fact 

 which appears inconsistent with any such affinity. 



In 1779 a highly important work on electricity 

 was published by lord Mahon, afterwards earl 

 of Stanhope. In this work the author enters at 

 large into the doctrine of electric atmospheres, 

 He showed, as had been previously done by Mr 

 Canton, that the air in the neigh bourliood of a 

 charged conductor gradually acquires the same 

 kind of electricity with the conductor, and that 

 the intensity of this state varies inversely as the 

 square of the distance from the conductor. 



In the same work he explained the nature of 

 what he called the returning stroke. When an 

 excited body is brought into the neighbourhood 

 of another body, the equilibrium of the electricity 

 in that body is disturbed. Let the first body bn 

 charged with positive electricity; the extremity 

 of the second body next it will become ncgativi ; 

 in consequence of the positive electricity of the 

 first body attracting the negative of the second 

 and repelling the positive, which last will accu- 

 mulate in the farthest extremity of the second 

 body. When matters are in this state, let tin 

 surplus electricity be discharged from the first 

 body by touching it with a conductor. The po- 

 sitive electricity which had accumulated at the 

 farthest extremity of the second body will now 

 return and spread itself equally over the whole 

 body. The same will happen to the nogalivc 

 electricity, which had accumulated in the enu 

 nearest the first body. It is to this return or new 

 distribution of the electricity that lord Stanhope 

 gave the name of returning stroke. Suppose a 

 largg cloud charged with positive electricity, ami 

 that one end approaches within a certain distrmc'O 



