Construction of Galvanic Magnets. 127 



2, or its effect as six times greater than that of the bar of iron. 

 Subsequent experiments confirm the great increase of power ob- 

 tained by componnd galvanic magnets. 



As it is difficult to magnetize a large mass of steel, and as it 

 is preferable to magnetize small bars and unite them into a com- 

 pound magnet, so it is found by experience to be very difficult 

 to magnetize by galvanism a large mass of iron to saturation ; 

 and the failure in a number of attempts to do so, together with 

 reasoning by analogy, led me to the construction of compound 

 galvanic magnets. A mass of iron, two inches in diameter, was 

 wound with a copper ribbon one half an inch wide, and one 

 hundred and twenty feet long. Upon being connected with a 

 small galvanic circle, containing half a square foot of zinc, it 

 lifted nearly fifty pounds. The same ribbon was then applied to 

 a horseshoe of soft iron, two feet long and one inch in diameter. 

 With the same battery and the same acid, the latter lifted one 

 hundred and fifty pounds. Both these magnets were of the 

 horseshoe form, and nearly of equal weights. This experiment 

 shows the difficulty of saturating with magnetism large masses 

 of iron ; but if we divide perpendicularly each extremity of the 

 large magnet into four equal parts, and wind each part separately, 

 there will be no difficulty in completely saturating the whole. 



Magnets made with hollow iron have been constructed and are 

 highly spoken of by some experimenters. With the same weight 

 of iron they may be made more powerful to a certain extent, 

 because more of the iron is brought near the winding and thus a 

 greater surface is brought near the action of the electrical current 

 but it soon reaches a maximum point. When the cavity is en- 

 larged, the circumference also must become larger, and a greater 

 length of wire or ribbon is required to go around it. On this ac- 

 count, with the same weight of wire, there must be a less num- 

 ber of layers of wire coiled around it, and the magnet will possess 

 less power. When the bore of a hollow magnet does not exceed 

 a certain size, its power must be greater than a solid magnet with 

 the same weight of iron, but this hollow magnet must be of less 

 power than when its cavity is filled up with soft iron. 



As the power of an electrical current resides principally in the 

 surface of the conductor, it would seem reasonable that if the 

 surface of the wire which is wound around galvanic magnets be 

 increased, its magnetic effects will be increased. This is true to 



