274 PROCEEDINGS OF THE AMERICAN ACADEMY 



XI. A coil of wire was now put about the middle of a piece of gas- 

 pipe, which was without permaneut magnetism. The \nece of pipe 

 was about 4 feet long and f of an inch in diameter. This, when in 

 connection with the telephone, was sti-uck two or three times a sec- 

 ond, with a piece of brass rod, and while being thus struck it was 

 rotated from the magnetic meridian to a position at right angles to it. 

 The difference in the loudness of the sound, between the position in 

 the meridian and away from it, was very marked. It is therefore 

 shown to be possible to determine the points of the compass with a 

 telephone, a coil, and an iron rod. 



XII. A second flexible ring was now made, about a foot in diame- 

 ter, consisting of a bundle of soft iron wire, the ends being roughly 

 braided and twisted together : the thickness of this was rather less 

 than half an inch. This was covered by a rubber tape wound spirally 

 round it, the better to secure stability of form and insulation. Then 

 4.6 ohms of No. 21 wire were wound about it its entire length, mak- 

 ing probably 1,000 turns. It was then magnetized by a current from 

 three secondary cells having six volts, giving a magnetizing current 

 of about 1,300 ampere turns, leaving it a ring magnet. The termi- 

 nals were then connected with the terminals of a reflecting galvan- 

 ometer with a resistance of .67 ohm. Very slight changes in the 

 form of the ring, either by pulling or pushing, gave decided move- 

 ments to the needle, while larger amplitude gave 30 to 40 degrees* 

 deflection. 



XIII. It was noticed, also, that the direction of the current de- 

 pended, not only upon the direction of the motion changing the form, 

 but also upon the direction of the motion with reference to the normal 

 shape of the ring. Thus, if the ring be a circle, and it be drawn into 

 a horizontal ellipse, the current will move the galvanometer needle, 

 say to the right. When it is brought back to the circular form, the 

 current is reversed. If the motion be continued so as to produce a 

 vertical ellipse, the current will be in the same direction as that pro- 

 duced at first by a motion exactly opposite in direction, so that for a 

 complete cycle of vibratory changes four currents are generated, two 

 direct and two reverse. 



XIV. One of the iron rings before mentioned, a heavy one about 

 eight inches in diameter and an inch and a half thick, having coarse 

 wire wound upon it nearly covering the ring, was connected with the 

 galvanometer as before, and the ring was struck by a brass rod. The 

 needle instantly swung through a wide angle. Struck again, it moved 

 as before, but not through so wide an angle, and a half-dozen blows 



