102 PEOCEEDINGS OF THE REGENTS. 



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 he^ 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 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 in- 

 crease of the number of turns. This was due to the increased resist- 

 ance 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, bul in using 

 a number of separate coils on the same piece of iron. By this ar- 

 rangement 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, 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 com- 

 pound 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 va- 

 riously combined in sets of lessser 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 battery of a single cup, a number of helices is required ; but 

 when a compound battery is used then one long wire must be em- 

 ployed, making many turns around the iron, the length of wire and 



