October io, 1890.] 



SCIENCE. 



brouglit into play, are qualifications admirably adapted for 

 their introduction into a variety of arrangements in which 

 powerful magnets so essentially operate, and perform a dis- 

 tinguished part in the production of electro-magnetic rota- 

 tions; whilst the versatilities of polarity of which they are 

 susceptible are eminently calculated to give a pleasing diver- 

 sity in the exhibition of that highly interesting class of phe- 

 nomena, and lead to the production of others inimitable by 

 any other means." ' 



Sturgeon's further work during the next three years is best 

 described in his own words: — ' 



"It does not appear that any very extensive experiments 

 were attempted to improve the lifting power of electro-mag- 

 nets from the time that my experiments were published in 

 the 'Transactions of the Society of Arts, etc.,' for 1825, till 

 the latter part of 1828. Mr. Watkins, philosophical-instru- 

 ment maker, Charing Cross, had, however, made them of 

 much larger size than any which I had employed, but I am 

 not aware to what extent he pursued the experiment. 



'.'In the year 1828, Professor Moll of Utrecht, being on a 

 visit to London, purchased of Mr. Watkins an electro-mag- 

 net weighing about 5 pounds, — at that time, I believe, the 

 largest which had been made. It was of round iron, about 

 one inch in diameter, and furnished with a single copper 

 wire twisted round it eighty-three times. When this magnet 

 was excited by a large galvanic surface, it supported about 75 

 pounds. Professor Moll afterwards prepared another electro 

 magnet, which, when bent, was 12| inches high, 2^ inches in 

 diameter, and weighed about 26 pounds, prepared like the 

 former with a single spiral conducting wire. With an act- 

 ing galvanic surface of 11 square feet, this magnet would 

 support 154 pounds, but would not lift an anvil which 

 weighed 200 pounds. 



"The largest electro-magnet which I have yet [18321 ?s;- 

 hibited in my lectures weighs about 16 pounds. It is formed 

 of a small bar of soft iron, 1^ inches across each side. The 

 cross-piece, which joins the poles, is from the same rod of 

 iron, and about 3| inches long. Twenty separate strands of 

 copper wire, each strand about 50 feet in length, are coiled 

 round the iron, one above another, from pole to pole, and 

 separated from each other by intervening cases of silk. The 

 first coil is only the thickness of one ply of silk from the 

 iron; the twentieth, or outermost, about half an inch from 

 it. By this mean the wii'es are completely insulated from 

 each other without the trouble of covering them with thread 

 or varnish. The ends of wire project about 2 feet for the 

 convenience of connection. With one of my small cylin- 

 drical batteries, exposing about 150 square inches of total 

 surface, this electro magnet supports 400 pounds. I ha^fe 

 tried it with a larger battery, but its energies do not seem to 

 be so materially exalted as might have been expected by 

 increasing the extent of galvanic surface. Much depends 

 upon a proper acid solution. Good nitric or nitrous acid, 

 with about six or eight times its quantity of water, answers 

 very well. With a new battery of the above dimensions 

 and a strong solution of salt and water, at a temperature of 

 190° F., the electromagnet supported between 70 and 80 

 pounds when the first seventeen coils only were in the cir- 

 cuit. With the three exterior coils alone in the circuit, it 

 would just support the lifter, or cross-piece. When the 

 ' sturgeon's Scientific Eesearches, p. 113. 



temperature of the solution was between 40° and 50"^, the 

 magnetic force excited was comparatively very feeble. With 

 the innermost coil alone and a strong acid solution, this 

 electro-magnet supports about 100 pounds; with the four 

 outermost wires, about 250 pounds. It improves in power- 

 with every additional coil until about the twelfth, but not 

 perceptibly any further: therefore the remaining eight coils 

 appear to be useless, although the last three, independently of 

 the innermost seventeen, and at the distance of half an 

 inch from the iron, produce in it a lifting-power of 75 

 pounds. 



" Mr. Marsh has Btted up a bar of iron much larger than 

 mine, with a similar distribution of the conducting wires to 

 that devised and so successfully employed by Professor 

 Henry. Mr. Marsh's electro-magnet will support about 560 

 pounds when excited by a galvanic battery similar to mine. 

 These two, I believe, are the most powerful electro magnets; 

 yet produced in this country. 



"A small electro-magnet, which I also employ on the- 

 lecture-table, and the manner of its suspension, are repre- 

 sented by Fig. 4. The magnet is of cylindric rod-iron, anJ- 

 weighs 4 ounces. Its poles are about a quarter of an inch 

 asunder. It is furnished with six coils of wire in the same 

 manner as the large electro-magnet before described, and 

 will support upwards of 50 pounds. 



"I find a triangular gin very convenient for the suspen- 

 sion of the magnet in these experiments. A stage of thin 

 board, supporting two wooden dishes, is fastened at a proper- 

 height to two of the legs of the gin. Mercury is placed ia 

 these vessels, and the dependent amalgamated extremities 

 of the conduciiug wires dip into it, — one into each portion. 



"The vessels are sufficiently wide to admit of considerable 

 motion of the wires in the mercury without interrupting the 

 contact, which is sometimes occasioned by the swinging of 

 the magnet and attached weight. The circuit is completed 

 by other wires, which connect the battery with these tw& 

 portions of mercury. When the vveight is supported as in 

 the figure, if an interruption be made by removing either of 

 the connecting wires, the weight instantaneously drops on 

 the table. The large magnet I suspend in the same way on 

 a larger gin. The weights which it supports are placed one 

 after another on a square board, suspended by means of a 

 cord at each corner from a hook in the cross-piece, which 

 joins the poles of the magnet. 



"With a new battery, and a solution of salt and water, at 

 a temperature of 190° F., the small electro-magnet (Fig. 3) 

 supports 16 pounds." 



In 1840, after Sturgeon had removed to Manchester, where 

 he assumed the management of the ''Victoria Gallery of 

 Practical Science," he continued his work, and in the seventh 

 memoir in his series of researches he wrote as follo^vs: — 



" The electro-magnet belonging to this institution is made 

 of a cylindrical bar of soft iron, bent into the form of a 

 horseshoe magnet, having the two branches parallel to each 

 other, and at the distance of 4| inches. The diameter of the 

 iron is 2f inches: it is 18 inches long when bent. It is sur- 

 rounded by fourteen coils of copper wire, — seven on each 

 branch. The wire which constitutes the coils is one-twelfth of 

 an inch in diameter, and in each coil there are about seventy 

 feet of wire. They are united in the usual way with branch 

 wires, for the purpose of conducting ihe currents from th& 



