126 



Construction of Galvanic Magnets. 



exert themselves at their own extremities. That this is the case 

 may be easily proved by experiment. Take any magnet, and 

 apply to one of its poles a piece of soft iron. This iron will have 

 considerable magnetic power while in contact with the magnet. 

 But the power of this iron is much less than that of the mag- 

 nets, and the longer the iron, the less is its power. 



If then we can bring into direct action the extremities of all 

 four of the parts of the magnet, Fig. 1, we shall increase the 

 power of the whole magnet while its weight remains the same. 

 This may be accomplished by means of compound galvanic mag- 

 nets constructed in the following manner. To the transverse bar 

 of iron, A B, Fig. 4, fasten, by welding, riveting, or screwing, the 



Fig. 4. 



four upright pieces of larger iron, C, D, E, F, and wind the whole, 

 either with wire or metaUic ribbon, in such a manner that the 

 poles, C and D, shall be of the same name, but of a different de- 

 nomination from E and F, which are also alike. Upon connect- 

 ing C, D, and E, F, with the plates of soft iron G, H, which act 

 as the armatures of compound steel magnets, we shall have the 

 whole converted into a compound galvanic magnet, which may 

 be supposed to represent the magnet Fig. 1, having the extrem- 

 ities of the four parts B, C, D, E, brought into direct action, and 

 the part A, forged out into a bar of half the thickness, and twice 

 the length, which acts as the connecting point between the com- 

 pound poles. Experiment proves the truth of the above reason- 

 ing. A bar of iron one foot in length, and weighing one pound, 

 was wound with a piece of metallic ribbon of copper foil, cov- 

 ered with silk. With a weak charge of a small galvanic arrange- 

 ment, it lifted a little less than one pound at each extremity. 

 The same ribbon was then wound around the iron of a com- 

 pound galvanic magnet, constructed as in Fig. 4, and weighing 

 four ounces ; with the same charge, and the same battery, this 

 last lifted three pounds. Now this experiment gives us the in- 

 crease of power in favor of the compound magnet as 3 x 4 is to 



