in Magnetism and Electricity. 87 



22. A second series of experiments was made with the view 

 of ascertaining the relation existing between the lifting-power 

 of the permanent magnets on the magnet-cylinder, and that of 

 an electromagnet excited by the electricity derived from the 

 magneto-electric machine. In these investigations the apparatus 

 shown in fig. 8 was used, which consisted of a small electro- 

 magnet, made by bolting to an iron block, forming the base of 

 the electromagnet, two plates of iron 6 inches long, 3 inches 

 wide, and Jths of an inch thick. The inside distance between 

 the two plates was about 2 inches ; and the polar surfaces of 

 the magnet were truly planed, as was also the under surface of 

 the keeper or submagnet used in connexion with it. This sub- 

 magnet was made of a small block of iron about 3 inches square 

 and 1 inch in thickness, and was connected, by means of a link 

 and swivel, to one end of a scale-beam supported at its centre 

 by an upright pillar. From the other end of the beam depended 

 a scale-pan, which was weighted so as to exactly counterbalance 

 the weight of the submagnet. The stand supporting the scale- 

 beam was firmly bolted to an iron lathe-bed, as was also the 

 electro-magnet, which was placed in a vertical position beneath 

 the submagnet. 



23. Around each side or plate of the electromagnet, a length 

 of 100 feet of insulated copper wire 0*05 of an inch in diameter 

 was coiled, and the ends of the wires were so arranged that they 

 could, at pleasure, be coupled up so as to form a single 

 circuit of 200 feet, or a double circuit of 100 feet in length. 

 One foot of the wire on the armature of the magneto-electric 

 machine had a resistance equal to 3 feet of the single wire on 

 the electro-magnet. 



24. Experiments were made, in the first instance, for the 

 purpose of ascertaining what influence the number of magnets 

 on the magnet-cylinder had upon the attractive force mutually 

 exerted by the electromagnet and the submagnet. As the 

 scale-beam was of too delicate a construction to allow of the 

 submagnet being placed in direct metallic contact with the 

 electromagnet, a piece of thin cardboard was fastened upon the 

 poles, by means of gum. The wires of the electro-magnet were 

 coupled up so as to form a double circuit 100 feet in length, 

 the resistance of which was about one-tenth of the resistance of 

 the armature circuit. The electromagnet was excited by the 

 direct current from the magneto- electric machine. The sub- 

 magnet was then placed upon the covered poles of the electro- 

 magnet, and small weights were introduced into the scale-pan 

 of the balance until the submagnet was separated from the 

 electromagnet. 



25. In order that a more rigid comparison might be made 



