209 



Prof. H. believes that it may be justly inferred, from these experi- 

 ments, that the attraction is due to ponderable matter, while the re- 

 pulsion 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 experiment 

 of Prof. Wheatstone's, Prof. H. 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 pane of glass dusted with red lead and sulphur ; 

 two figures of positive and negative electricity were produced. 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 i!ew 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. H.'s first expeiiment 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, 

 though not at so great distances as the dynamical. He then ex- 

 plained his views of the nature of dynamical induction. When a 

 spark is thrown upon a wire, it passes in a wave, whose length might 

 be determined if we knew the velocity of electricity ; now, if we have 

 another parallel wire, a negative wave will be formed in this, and the 

 two waves will travel simultaneously in the same direction. But this 

 is equivalent to a positive induced wave in the opposite direction. In 

 this way the phenomena accompanying the discharge of a jar are 

 easily explained. Again, if we conceive that in a galvanic battery 

 the discharge consists of a series of such waves, we may very simply 

 explain the phenomena of galvanic induction. 



Mr. Justice stated, that within the last six months he had 

 planned two observatory buildings, which, so far, had been 



