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 LVIII. Litelligence and Miscellajieoiis Articles. 



ELECTRICAL EXPERIMENTS. 



TJl^OF. HENRY, of Princeton, communicated to the American 

 -^ Philosophical Society the result of a series of experiments on 

 electricity made last winter. They had reference, first, to the dis- 

 charge of electricity through a long wire, connected with the earth 

 at the farther end; secondly, to the discharge of a jar through a 

 wire ; and thirdly, to an attempt to account for the phaenomena of 

 dynamic induction. 



Prof. Henry first showed, that when a charge of electricity is 

 given to one end of a wire, the diflTerent parts of the wire become 

 charged successively, as though a wave of electricity passed along it. 

 He then showed that the charge passed along the surface of the 

 wire, and not through its whole mass, as was supposed from the 

 analogy of galvanic conduction. Hence he inferred that dynamical 

 electricity obeys the same laws as the statical. He then detailed 

 some experiments upon the passage of electricity through plates, and 

 showed that when a charge was transmitted across a plate, the ten- 

 sion was greatest at the edges, the electricity apparently exercising a 

 self-repelling action, while, if the charge were passed through two 

 pieces of tinfoil, these slips attract each other. 



Prof. Henry believes that it may be justly inferred, from these ex- 

 periments, that the attraction is due to ponderable matter, while the 

 repulsion is due to electricity ; thus showing that electricity is a sepa- 

 rate principle, and not a mere property of matter. 



Prof. Henry next passed to the subject of the discharge of a jar. 

 It was necessary, in his experiments, to get rid of the free electricity 

 arising from the thickness of the glass, and it occurred to him that 

 this might be done by removing the knob, and making the coating 

 upon the inside of less area than that upon the outside. With this 

 arrangement, when the discharge was made through a long wire, and 

 a test jar brought near it during discharge, a bright spark passed ; but 

 upon approaching the jar to a delicate electrometer, it gave no indica- 

 tions of free electricity. Reflecting upon this, and upon an experi- 

 ment of Prof. Wheatstone, he was led to believe that the jar is dis- 

 charged by two waves, a negative and a positive one, starting simul- 

 taneously from the two ends of the wire. To prove this, he broke 

 the wire, and interposed a jjane of glass dusted with red lead and 

 sulphur ; two figures of positive and negative electricity were pro- 

 duced. He made several other experiments tending to prove this 

 same fact. He showed how these experiments serve to explain that 

 of Dr. Priestley, where a spark was found to pass between the ends 

 of a long bent wire, the ends being brought within a few inches of 

 each other. 



He next passed to the connexion between statical and dynamical 

 induction. Statical induction has heretofore only been observed at 

 short distances. Prof. Henry's first experiment proved that it could be 

 observed at the distance of nineteen feet, the floor of a chamber inter- 

 vening, showing that statical induction takes place at great distances. 



