ADDRESS OF PROF. A. M. MAYER. 483 



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, an experimental magnet 

 was constructed. 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 battery of a single cup, a number of helices is required ; but 

 when a compound 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 quantity magnets were introduced to avoid circumlocution, and 

 were intended to be used merely in a technical sense. By the 

 intensity magnet I designated a piece of soft iron, so surrounded with 

 wire that its magnetic power could be called into operation by an 

 intensity battery ; and by a quantity magnet a piece of iron so sur- 

 rounded by a number of separate coils that its magnetism could be 

 fully developed by a quantity battery. 



"I was," says Henry, "the first to point out this connection of 

 the two kinds of the battery with the two forms of the magnet, in 

 my paper in Silliman's Journal, January, 1831, and clearly to state 

 that when magnetism was to be developed by means of a compound 

 battery, one long coil was to be employed, and when the maximum 

 effect was to be produced by a single battery, a number of strands 

 \vere to be used." 



Here is Henry's description of one of his quantity magnets : " A 

 bar of iron 21 inches long and 2 inches square with rounded corners 

 was bent into a U form, having legs about 9 inches long. This bar 

 weighed 21 pounds. Its armature was formed of a piece of a similar 



