200 



SCIENCE. 



[Vol. XVI. No. 401 



net is seen sideways, supporting a bar of iron, y. The cir- 

 cuit was completed to the battery through a connecting 

 wire, d, which could be lifted out of the cup Z, so breaking 

 circuit when desired, and allowing the weight to di'op. 

 Sturgeon _added in his explanatory I'emarks that the poles, 

 N and S, of the magnet will be reversed if you wrap the 

 copper wire about the rod as a right-handed sci-ew instead of 

 a left-handed one, or, more simply, by reversing the conuec- 



FIG. 3. — STURGEONS STRAIGHT-BAR ELECTRO-MAGNET. 



tions'with'the battery, by causing the wire that dips into the 

 Z cup to dip into the C cup, and vice versa. This electro- 

 magnet was capable of supporting nine pounds when thus 

 excited. 



Fig. 3 shows another arrangement to fit on the same stand. 

 This arrangement communicates magnetism to hardened 

 steel bars as soon as they are put in, and renders soft iron 

 within it magnetic during the time of action. It only differs 



FIG. 4. — STURGEON'S LECTURE-TABLE ELECTRO-MAGNET. 



from Figs. 1 and 3 in being straight, and thereby allows the 

 steel or iron bars to slide in and out. 



For this piece of apparatus and other adjuncts accompany- 

 ing it, all of -which are described in the society's "Transac- 

 tions" for 1825, Sturgeon, as already stated, was awarded 

 the society's silver medal and a premium of thirty guineas. 

 The apparatus was deposited in the museum of the society, 

 which therefore might be supposed to be the proud possessor 

 of the first electro-magnet ever constructed. Alas for the 

 vanity of human affairs! the society's museum of apparatus 



has long been dispersed, this priceless relic having been 

 either made over to the now defunct Patent Office Museum, 

 or otherwise lost sight of. 



Sturgeon's first electro-magnet, the core of which weighed 

 about 7 ounces, was able to sustain a load of 9 pounds, or 

 about twenty times its own weight. At the time it was con- 

 sidered a truly remarkable performance. Its single layer of 

 stout copper wire was well adapted to the battery employed, 

 a single cell of Sturgeon's own particular construction having 

 a surface of 130 square inches, and therefore of small internal 

 resistance. Subsequently, in the hands of Joule, the same 

 elfctro-mpgnet sustained a load of 50 pounds, or about a hun- 

 dred and fourteen times its own weight. Writing in 1832 

 about his apparatus of 1825, Sturgeon used the following 

 magniloquent language: — 



" When first I showed that the magnetic energies of a 

 galvanic conducting wire are more conspicuously exhibited 

 by exercising them on soft iron than on hard steel, my ex- 

 periments were limited to small masses, generally to a few 

 inches of rod-iron about half au inch in diameter. Some of 

 those pieces were employed while straight, and others were 

 bent into the form of a horseshoe magnet, each piece being 

 encompassed by a spiral conductor of copper wire. The 

 magnetic energies developed by these simple arrangements 

 are of a very distinguished and exalted character, as is con- 

 spicuously manifested by the suspension of a considerable 

 weight at the poles during the period of excitation by the 

 electric influence. 



"An unparalleled transiliency of magnetic action is also 

 displayed in soft iron by an instantaneous transition from a 

 state of total inactivity to that of vigorous polarity, and also 

 by a simultaneous reciprocity of polarity in the extremities 

 of the bar, — versatilities in this branch of physics for the 

 display of which soft iron is pre-eminently qualified, and 

 which, by the agency of electricity, become demonstrable 

 with the celerity of thought, and illustrated by experiments 

 the most splendid in magnetics. It is, moreover, abundantly 

 manifested by ample experiments that galvanic electricity 

 exercises a superlative degree of excitation on the latent 

 magnetism of soft iron, and calls for its recondite powers 

 with astonishing promptitude, to an intensity of action far 

 surpassing any thing which can be accomplished by any 

 known application of the most vigorous permanent magnet, 

 or by any other mode of experimenting hitherto discovered. 

 It has been observed, however, by experimenting on different 

 pieces selected from various sources, that, notwithstanding 

 the greatest care be observed in preparing them of a uniform 

 figure and dimensions, there appears a considerable differ- 

 ence in the susceptibility which they individually possess of 

 developing the magnet powers, much of which depends upon 

 the manner of treatment at the forge, as well as upon the 

 natural character of the iron itself.' 



"The superlative intensity of electro-magnets, and the 

 facility and promptitude with which their energies can be 



1 ''I have made a number of experiments on small pieces, from the results 

 of which it appears that much hammering Is highly detrimental to the develop- 

 ment of magnetism In soft Iron, whether the exciting cause be galvanic or any 

 other; and although good annealing is always essential, and facilitates to a 

 considerable extent the display of polarity, that process Is very far from re- 

 storing to the iron that degree of susceptibility which it frequently loses by 

 the operation of the hammer. Cyllndric rod-iron o£ small dimensions may 

 very easily bo bent into the required form without any hammering whatever; 

 and I have found that small electro-magnets made in this way display the 

 magnetic powers in a very exalted degree." 



