492 Prof. J. Henry's Contributions 



when the contact with the water is made in a line at right 

 angles to the last, only a slight sensation is felt in each hanti, 

 but no shock. 



31. Since the publication of my last paper, I have exhibited 

 to my class the experiment (No. III. Sect. III.) relative to the 

 induction at a distance on a much larger scale. All my coils 

 were united so as to form a single length of conductor of 

 about four hundred feet, and this was rolled into a ring of 

 five and a half feet in diameter, and suspended vertically 

 against the inside of the large folding doors which separate 

 the laboratory from the lecture-room. On the other side of 

 the doors, in the lecture-room, and directly opposite the coil, 

 was placed a helix, formed of upwards of a mile of copper 

 wire, one-sixteenth of an inch in thickness, and wound into 

 a hoop of four feet in diameter. With this arrangement, and 

 a battery of one hundred and forty-seven square feet of zinc 

 surface divided into eight elements, shocks were perceptible 

 in the tongue, when the two conductors were separated, to 

 the distance of nearly seven feet; at the distance of between 

 three and four feet, the shocks were quite severe. The ex- 

 hibition was rendered more interesting by causing the induc- 

 tion to take place through a number of persons standing in a 

 row between the two conductors. 



Sect. II. — On apfarenthj tiao kinds of Elect i o- dynamic 

 Induction. 



32. The investigations arranged under this head had their 

 origin in the following circumstances. Alter the publication 

 of my last paper, I received, through the kindness of Dr. 

 Faraday, a copy of the fourteenth series of his researches, 

 and in this I was surprised to find a statement which appeared 

 in direct opposition to one of the principal facts of my com- 

 munication. In paragraph 59, 1 state, in substance, that 

 when a plate of metal is interposed between the coil trans- 

 mitting a galvanic current, and the helix placed above it to 

 receive the induction, the shock from the secondary current 

 is almost perfectly neutralized. Dr. Faraday, in the exten- 

 sion of his new and ingenidus views of the agency of the in- 

 termediate particles in transmitting induction, was led to make 

 an experiment on the same point; and apparently, under the 

 same circumstances, he found that it " makes not the least 

 difference, whether the intervening space between the two 

 conductors is occupied by such insulating bodies as air, sul- 

 phur, and shell-lac, or such conducting bodies as copper and 

 other non-magnetic metals." 



33. As the investigation of the fact mentioned above tbrnis 



