PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 529 



•electricity derived from tlie urmatiirc. When four permanent 

 magnets capable of sustaining 40 lbs. and the sul)-magiiets were 

 placed in metallic contact with the poles of the electro-magnet, a 

 weight of 178 lbs. was required to sepai'ate them. With a larger 

 electro-UKignet, not less than 1,080 lb.s. was reqnired; thiit is, the 

 ■electro-magnet Imd an attr:w^tive force twenty-seven times greater 

 than the combined force of the four permanent magnets. It is 

 further found that the power of the electro-magnet nniy, in the 

 same manner, be indetiiiitely increased. 



By experimenting with electro-nmgnets of various sizes, it was 

 found that when the wires forming the polar terminals of the 

 magneto-electric machine were connected with a large electro- 

 magnet but a short time, a spark coidd be obtained from the 

 electro helices twenty-five seconds after sucii connection had Ijeen 

 broken. Hence, Mr. Wilde infers that an electro-magnet possesses 

 the power of accumulating and retaining a charge of electricity 

 similar but not ideutical Avith that whii^h is retained iu insulated 

 submarine cables, and in the Leyden jar. 



It may here be remarked that the discovery of the accumulating 

 and retaining power of an electro-magnet is not new : it was long 

 since demonstrated in this country by experimenters who had con- 

 structed lar^e elec ro-magnets, under the impression that the same 

 results would follow, with them as with small magnets, and large 

 sums of money were expended before it was ascertained that the 

 time of the demagnetizing a magnet increases with its size, 



Mr. Wilde then proceeded to ascertain Avhether a proporlion- 

 ■ately large amount of dynamic electricity could be evolved by a 

 large electro-magnet excited by a small magneto-electric machine. 

 Two magnet-cyliudei's were made, having a l>ore of two and a half 

 inches and a length of twelve and a half inches. Each cylinder 

 was fitted with an armature, round which was insulated copper 

 wire 0.15 of an inch in diameter and sixty-seven feet in length. 

 Upon one magnet-cylinder sixteen permanent magnets were fixed, 

 and to the sides of the other magnet-cylinder was bolted an elec- 

 tro-magnet, formed of two rectangular pieces of boiler-plate enve- 

 loped with coils of insulated copper wire. The armatures of the 

 two and a half inches raao:neto-electric and the electro-magnetic 

 machines were simultaneously driven Avith an equal velocity of 

 2,500 vibrations per minute. When the electricity from the mag- 

 neto-electric machine was transmitted directly throng a piece of 



[Am. Inst.] HH 



