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In the arrangement of Arago and Sturgeon the several turns of wire 

 Avere not precisely at right angles to the axis of the rod, as they should 

 be, to produce the effect required by 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 multi- 

 plicity 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 electricity. Two methods of 

 improvement therefore suggested themselves. The first consisted, not in 

 increasing the length of the coil, but in using a number of separate coils 

 on the same piece of iron. By this arrangement the resistance to the 

 conduction of the electricity was diminished and a greater quantity made 

 to circulate 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, 

 Fig. 6. 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 number of compound 

 helices were placed on the same bar, their ends 

 left projecting, and so numbered that they could 

 be all united into one long helix, or variously combined in sets of lesser 

 length. 



From a series of experiments with this and other magnets it was proved 

 that, in order to produce the greatest amount of magnetism from a bat- 

 tery of a single cup, a number of helices is required ; but when a com- 

 pound battery is used, then one long wire must be employed, making many 

 turns around the iron, the length of wire and consequently the number of 

 turns being commensurate with the projectile power of the battery. 



In describing the results of my experiments, the terms intensity and 



