Arr.usT 15. 1907J 



NA TURE 



39: 



ntverlheli:ss they demonstrated the essential principle, and 

 suggested further possibilities. Two years later, Barlow, 

 using a star-wheel of copper, pivoted so that the lowest 

 point of the star should malce contact with a small pool 

 of mercury, found that the star-wheel rotated if a current 

 was sent through the arm of the star while the arm 

 itself was situated between the poles of a steel horseshoe- 

 magnet. Shortly ;)fterwards Sturgeon improved the 

 apparatus by substituting a copper disc for the star- 

 wheel. The action was the same. A conductor, carry- 

 ing an electric current, if placed in a magnetic field, is 

 found to experience a mechanical drag, which is neither 

 an attraction nor a repulsion, but a lateral force tending 

 to move it at right angles to the direction of flow of 

 the current and at right angles to the direction of the 

 lines of the magnetic field in which it is situated. Still 

 this was a tov. Two vears later came the announcement 

 bv Sturgeon of the invention of the soft-iron electro- 

 magnet, one of the most momentous of all inventions, 

 since upon it practically the whole of the constructive part 

 of electrical engineering is based. For the first time man- 

 kind was furnished with a magnet the attractive power 

 of which could be increased absolutely indefinitely by the 

 mere expenditure of sufficient capital upon the iron core 

 and its surrounding copper coils, and the provision of a 

 sufficiently pow-erful source of electric current to e.xcite 

 the magnetisation. Furthermore the magnet was under 

 control, and could be made to attract or to cease to attract 

 at will bv merely switching the current on or off ; and, 

 lastlv, this could be accomplished from a distance, even 

 from great distances away. How slowly the importance 

 of this discovery was recognised is now a matter for 

 astonishment. To state that Sturgeon died in poverty 

 twentv-six years later is sufficient to indicate his place 

 among the unrequited pioneers of whom the world is not 

 worthv. Six years elapsed, and then there came a flood 

 of suggestions of electric motors in which was applied 

 the principle of intermittent attraction by an electro- 

 magnet. Henry in 1831 and Dal Negro in 1832 produced 

 see-saw mechanisms so operated. Ritchie in 1S33 and 

 Jacobi in 1S34 devised rotatory motors. Ritchie pivoted a 

 rapidlv commutated electromagnet between the poles of a 

 permanent magnet — a true type of the modern motor — 

 while Jacobi caused two multipolar electromagnets, one 

 fixed, one movable, to put a shaft into rotation and propel 

 a boat. \ perplexing diminution of the current of the 

 battery whenever the motor was running caused Jacobi 

 to investigate mathematically the theory of its action. In 

 a masterly memoir he laid down a few years later the 

 theorv of electric motive power. But in the intervening 

 period, in 1831, Faraday had made the cardinal discovery 

 of the mechanical generation of electric currents by 

 magneto-electric induction, the fundamental principle of 

 the dynamo. Down to that date the onlv known way — 

 save for the feeble currents of thermopiles — to generate 

 electric currents had been the pile of Volta, or one of 

 the forms of battery which had been evolved from it. 

 Now, bv Faradav's discovery, the world had become 

 possessed of a new source, .''ind yet again, strange as it 

 mav seem, vears elapsed before the world — that is, the 

 world of engineers — discovered that an important discovery 

 had been made. Not until some thirty years later were 

 any magneto-electric machines made of a sufficient size 

 to be of practical service even in telegraphy, and none 

 were built of a sufficient power to furnish a single electric 

 light until about the year 1857. In the meantime in 

 .America other electric motors, to be driven by batteries, 

 had been devised by Davenport and by Page ; the tatter's 

 machine had an iron plunger to be sucked by electro- 

 magnetic attraction into a hollow coil of copper wire, 

 thereby driving a shaft and flywheel through the inter- 

 mediate action of a connecting-rod and crank. Page's 

 was. in fact, an electric engine, with 2-foot stroI<e, single- 

 acting, of between 3 and 4 horse-power. The battery 

 occupied about 3 cubic feet and consumed, according to 

 Page, 3 lb. of zinc per horse-power per dav. This must 

 have been an under-estimate : for if Daniell's cells were 

 used the minimum consumption for a motor of 100 per 

 cent, etliciency is known to be about 2 lb. of zinc per 

 horse-power per hour. 



NO. 1972, VOL. 76] 



Electric Motive i'oa'cc Impossible in 1857. 

 Upon the state of development of electric motors _ fifty 

 vears ago information may be gleaned from an exceedingly 

 interesting debate at the' Institution of Civil Engineers 

 upon a paper read April 21, 1857, "On Electromagnetism 

 as a Motive Power," by Mr. Robert Hunt, F.R.S. In 

 this paper the author states that, though long-enduring 

 thought has been brought to bear upon the subject, and 

 large sums of money have been expended on the construc- 

 tion of machines, "' yet there does not appear to be any 

 nearer approach to a satisfactory result than there w^as 

 thirty vears ago." .After e.xplaining the elementary prin- 

 ciples of electromagnetism, he describes the early motors 

 of Dal Negro, Jacobi, Davenport, Davidson, Page, and 

 others. Reviewing these and their non-success as com- 

 mercial machines, he says : " Notwithstanding these 

 numerous trials ... it does not appear that any satis- 

 factot*V explanation has ever been given of the causes 

 which' have led to the abandonment of the idea of employ- 

 ing electricity as a motive power. It is mainly with the 

 view of directing attention to these causes that the present 

 communication has been written." He admits that electro- 

 magnets may be constructed to give any desired liftmg 

 power; but he finds that the attractive force on the iron 

 keeper of a magnet of his own, which held 220 lb. when 

 in contact, fell to 36 lb. when the distance apart was only 

 one-fiftieth of an inch. To this rapid falling off of force 

 and to the hardening action on the iron of the repeated 

 vibrations due to the" mechanical concussion of the keeper, 

 he attributed the small power of the apparatus. .Also he 

 remarked upon the diminution of the current which is 

 observed to flow from the batterv when the motor was 

 running (which Jacobi had, in his memoir on the theory, 

 traced '^to a counter electromotive force generated m the 

 motor itself), and which reduced the effort exerted bv the 

 electromagnets ; this diminution he regarded as impairmg 

 the efficiencv of the machine. " All electromagnetic 

 arrangements'," he says, " sufi'er from the cause named, 

 a reduction of the mechanical value of the prime mover, 

 in a manner which has no resemblance to any of the effects 

 due to heat regarded as a motive power." Proceeding to 

 discuss the batteries, he remarked that as animal power 

 depends on food, and steam power on coal, so electric 

 power depends on the amount of zinc consumed ; in sup- 

 port of which proposition he cited the experiments of 

 Joule. He gives as his own results that for every grain 

 of zinc consumed in the batterv his motor performed a 

 dutv equivalent to lifting 86 lb. i foot high. Joule and 

 Scoresbv, using Daniell's cells, had found the duty to be 

 equivalent to raising 80 lb. i foot high, being about half 

 the theoretical maximum dutv for i grain of zinc. In the 

 Cornish engine, doing its best duty, i grain of coal w-as 

 equivalent to a dutv of raising 143 lb. i foot high He 

 put the price of zinc at 35/. per ton as compared with coa! 

 at less than 1/. per ton, which makes the cost of power 

 produced bv an electric motor— if computed by the con- 

 sumption of zinc in a batterv— about sixty times as great 

 as that of an eoual power produced by a steam-engine 

 consuming coal. He concludes that " it would be far more 

 economical to burn zinc under a boiler and to use it for 

 generating steam power than to consume zinc in a battery 

 for generating electromagnetical power." 



In the discussion which followed, several men of dis- 

 tinction took part. Prof. William Thomson, of Glasgow 

 (Lord Kelvin), wrote, referring to the results of Joule and 

 Scoresbv • " These facts were of the highest importance 

 in estimating the applicabilitv of electromagnetism, as a 

 motive power, in practice; and, indeed, the researches 

 alluded to rendered the theorv of the duty of electro- 

 magnetic engines as complete as that of the duty of water- 

 whwls was generallv admitted to be. Among other con- 

 clusions which might be drawn from these experiments 

 was this: that, until some mode of producing electncitv 

 .ns manv times cheaper than that of an ordmary galvanic 

 batterv as coal was cheaper than zinc, electromagnetic 

 engines could not supersede the steam-engine. Mr^ 

 W R. Grove (Lord Justice Sir William Grove) remarked 

 that a practical application of the science appeared to be 

 still distant. The great desideratum, in his opinion, was 

 not so much improvement in the machine as in the prime 



