1840] WRITINGS OF JOSEPH HENRY. 161 



maj^ be the worth of this suggestion, the secondary current 

 affords the means of imitating the phenomena of the shock 

 from the electrical eel, as described by Dr. Faraday. By 

 immersing the apparatus (Fig. 3) in a shallow vessel of 

 water, the handles being placed at the two extremities of the 

 diameter of the helix, and the hands plunged into the water 

 parallel to a line joining the two poles, a shock is felt through 

 the arms; but 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 hand, but no shock. 



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

 ited to my class the experiment (No. Ill, Sec. 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 per- 

 ceptible in the tongue, when the two conductors were sep- 

 arated, to the distance of nearly seven feet ; at the distance 

 of between three and four feet, the shocks were quite severe. 

 The exhibition was rendered more interesting by causing 

 the induction to take place through a number of persons 

 standing in a row between the two conductors. 



SECTION II. 



On apparently two Mnds of Electro-dynamic Induction. 



32. The investigations arranged under this head had their 

 origin in the following circumstances. After 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 ap- 



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