Researches in electro-magnetism
American Journal of Science
A. M. Mayer-Researches in ART. XX.-Researches in Electro-Magnetism; by ALFRED M. MAYER, Ph.D. A. M. Mayer-Researches in Electro-Magnetz'sm. impossibility of obtaining a current so constant as not to produce continual motion and vibration of the needle caused me to devise the following method, which I have found from experience to be both sensitive and precise. Apparatus for the comparative measures of electro-magnetic forces. -On a table 10 ft. long was drawn a center line and divided into
... d divided into fractions of an inch. This line was then accurately placed at right angles to the magnetic meridian. Two helices, which I designate as E and W, were placed 8 ft. apart with their axes in the same vertical plane as the above line. A surveyor's compass, with a senshive needle 5'85 in. long was so arranged that the point of suspension of the needle could be moved between the helices in the line of their axes. The same battery current passed through both helices, and in such direction that the N. . pole of each was facing the needle; by reversing the eurrent, the S. poles could be opposed to each other. Both helices were composed of10 layers of '1 inch" extra covered" copper wire, wrapped on copper spools of 8f inches long, 1'82 inches (liam., and having flanges at the ends 1'25 inches high. These spools, with their flanges, were split in the direetion of their length by an opening of 1'0 inch. Each layer of coils was saturated with a thick solution of shellac in alcohol and covered with thick paper, coated with shellac, before the succeeding layer was wrapped. Helix E contains 557'5 feet of wire in 696 turns, and on account of its better insulation and greater number of turns is superior in strength to helix W. Helix W contains 551 feet of wire in 688 turns.