224 ELECTRO-MOTIVE ENGINES 



ELECTRO-MOTIVE E3JGZKTES. Tho following remarks on this subject arc 

 an abstract of a communication read by tho editor to tho Institution of Civil Engi- 

 neers, for which they awarded him their Telford Medal. 



Numerous electro-magnetic machines havo been made, but a few only of these 

 require to be described. In 1832, Salvatore dal Negro published an account of tho 

 attempts made by him in this direction. As Dal Negro's engine was of a very simple 

 and effective kind, tho Professor's description of it may be quoted : ' As I had been 

 successful in producing temporary magnets of very great power, with very small elec- 

 tro-motors, I endeavoured to apply this power to moving machinery. I will now 

 briefly state by what means I endeavoured to set a lever in motion. I first used a 

 magnetic steel bar, placed vertically between one end of a temporary magnet. The 

 bar vibrated from the attractions and repulsions which took place between its north 

 polo and tho north and south poles of tho electro-magnet. In tho same way a motion 

 may be effected in a horizontal piano. I also set in motion a similar bar, by allowing 

 a piece of iron, set free from the magnet at tho moment when its power became = 

 to fall on one of its ends, after this it was immediately re-attracted. This can bo 

 effected in two ways : the one may be employed when a quick motion is to be produced, 

 and the second when a greater force is wanted ; in the first case the weight falls only 

 just out of tho power of tho magnet's attraction, and the instant the weight has fallen 

 upon tho bar, or lever, it is re-attracted by the magnet that the action may be re- 

 peated : it is always small in comparison with that which tho magnet cannot support 

 whilst in contact. In the second case the whole weight which the magnet can carry 

 is employed, and use is made of the force which draws it to tho magnet.' Upon this 

 was founded several other attempts, particularly one by Dr. Schulthess, who was so 

 satisfied with the result, that he wrote in 1833 : 'If we consider that electro-magnets 

 have already been made, which were capable of carrying 20 cwts., and that there is 

 no reason to doubt that they may bo made infinitely more powerful, I think I may 

 boldly assert that electro-magnetism may certainly be employed for the purpose of 

 moving machines. Professor Botto, of Turin, also employed ' a lever put in motion 

 (in the manner of a metronome) by the alternating of two fixed electro-magnetic 

 cylinders, exerted on a third moveablc cylinder, connected with the lower arm of the 

 lever, the upper part of which maintains a metallic wheel, serving in the ordinary 

 way, as a regulator in a continuous gyratory motion.' It will be evident to any one 

 who has observed the motion of many of the electric clocks, that this is in several 

 respects similar to the pendulous motions adopted. 



In 1835, tho late Prof. Jacobi, of St. Petersburg, published an account of his expe- 

 riments, which were carried out on a largo scale, regardless of cost, at the expense 

 of the Emperor Nicholas. His first idea was to employ the attractive and repellant 

 powers of magnetic bars, so that he might obtain an advancing and receding motion, 

 which could be easily changed into a continuous circular motion. A great many 

 machines havo been made upon this principle ; but Jacobi alone, as far as can bo 

 learned, has pointed out the true cause of their failure. ' We know,' he says, tho 

 ill effects of shocks in the movements of machines, but there is here another incon- 

 venience which is not simply mechanical. The soft iron, by these repeated shocks 

 and vibrations, gradually acquires at the surface of contact tho nature of steel ; there 

 will be a considerable permanent magnetism, and the transient magnetic force which 

 alone produces the movement, will bo weakened in proportion. A number of ex- 

 periments, which I havo made upon tho magnetic force of a bar of soft iron, bent 

 into a horseshoe form, has shown me tho great disadvantage of often-repeated shocks, 

 proceeding from tho sudden contact of tho armature.' 



Jacobi, finally setting aside all oscillating motions, produced a machine giving con- 

 tinuous circular motion, by fixing eight electro-magnetic bars on a disc, movoable round 

 an axis and eight fixed bara similarly arranged upon a fixed platform. The ari'.-ui^c- 

 ment of the bars admitted of much variety, provided it was exactly symmetrical, and 

 that it allowed the poles to approach each other as nearly as possible. Arrangements 

 were made, with much ingenuity, by which tho poles of tho magnets were inversed 

 directly, and so that inversion should take place precisely at that point where 

 the bars were opposite each other. One hundred and forty-four inversions in the 

 second were readily effected, and Jacobi declared it would bo easy with his apparatus 

 to change, or to completely interrupt, the electric current one thousand or more 

 times in a second. 



A machine constructed upon this principle was, at tho doeiro and at the cost of an 

 Imperial Commission, put on board a ten-oared shallop, equipped with paddle-wheels, 

 to which the electro-magnetic machine communicated motion. Tho boat was 28 feet 

 long, and 7J feet in width, and drew 2.} feet of water. In general, there were 10 or 

 12 persons on board, and the voyage on tho Neva was continued during several entire 

 days. By these experiments Jacobi was led to tho conclusion that a battery of 



