I 



128 Contributions to Electricity and Magnetism. 



30. In this connexion I may mention that the idea has occur- 

 red to me that the intense shocks given by the electrical fish may 

 possibly be from a secondary current, and that the great amount 

 of nervous organization found in these animals may serve the 

 purpose of a long conductor.* It appears to me, that in the pres- 

 ent state of knowledge, this is the only way in which we can 

 conceive of such intense electricity being produced in organs im- 

 perfectly insulated and immersed in a conducting medium. But 

 Ave have seen that an original current of feeble intensity can in- ■ 

 duce, in a long wire, a secondary current capable of giving in- 1 

 tense shocks, although the several strands of the wire are sepa- 

 rated from each other only by a covering of cotton thread. 

 Whatever may be the worth of this suggestion, the secondary cur- 

 rent affords the means of imitating the phenomena of the shock 

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

 sing the apparatus (Fig. 3,) in a shallow vessel of water, the han- 

 dles being placed at the two extremities of the diameter of the he- 

 lix, 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 exhibited to 

 my class the experiment, (No. Ill, Sec. 3d,) relative to the induc- 

 tion at a distance on a much larger scale. All my coils were uni- 

 ted so as to form a single length of conductor of about four hun- 

 dred 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 ar- 

 rangement, 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 separated, to 

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

 and four feet, the shocks were quite severe. The exhibition was 



* Since writing the above, I have found that M. Masson has suggested the same 

 idea, in an interesting thesis lately published. 



