430 WRITINGS OF JOSEPH HENRY. [1857 



In the arrangement of Arago and Sturgeon the several 

 turns of wire were not precisely at right angles to the axis 

 of the rod, as they should be — to produce the effect required 

 b}' the theory, but slightly oblique, and therefore each 

 tended to develop a separate magnetism not coincident with 

 the axis of the bar. But in winding the wire over itself, the 

 obliquity of the several turns compensated each other, and 

 the resultant action was at right angles to the bar. The 

 arrangement then introduced by myself was superior to 

 those of Arago and Sturgeon, first in the greater multiplicity 

 of turns of wire, and second in the better application of these 

 turns to the development of magnetism. The power of the 

 instrument, with the same amount of galvanic force, was by 

 this arrangement several times increased. 



The maximum effect however with this arrangement and 

 a single battery was not yet obtained. After a certain length 

 of wire had been coiled upon the iron, the power diminished 

 with a further increase of the number of turns. This was 

 due to the increased resistance which the longer wire offered 

 to the conduction of electricit3\ Two methods of improve- 

 ment therefore suggested themselves. The first consisted — 

 not in increasing the length of the coil, but in using a num- 

 ber of separate coils on the same piece of iron. By this 

 arrangement the resistance to the conduction of the elec- 

 tricity was diminished, and a greater quantity made to cir- 

 culate around the iron from the same battery. The second 

 method of producing a similar result consisted in increasing 

 the number of elements of the battery, or in other, words 

 the projectile force of the electricity, which enabled it to 

 pass through an increased number of turns 

 of wire, and thus by increasing the length 

 of the wire, to develop the maximum power 

 of the iron. 



To test these principles on a larger scale, 

 the experimental magnet was constructed, 

 which is shown in figure 6. In this a num- 

 ber of compound helices was placed on the Fig. 6. 

 same bar, their ends left projecting, and so numbered that 



