Prime Movers. 23 



tensity is required, only because of the resistance which a great 

 length of wire offers to the current. If heat and electricity are 

 not merely modifications of the same element they are certainly 

 most intimately connected, and are always found associated. 



Besides all this, the force of electro-magnets diminishes 

 rapidly through space. One which retained two hundred 

 pounds in contact, at one-fiftieth of an inch, lifted only forty 

 pounds and a-half, or about one-fifth. Also, the disturbance 

 caused by the motion of the electro-magnet, or of its sub- 

 magnet, greatly diminishes the power. A magnet which, when 

 free from disturbance, possessed a force of one hundred and 

 fifty pounds, fell to one-half when the sub-magnet, or armature, 

 was made to revolve near its poles. Moreover, the very change 

 of the electric current causes a diminution of its effect : since 

 the secondary current which is generated moves in a direction 

 opposite to that which produces the required motion. Time 

 also is necessary for magnetization ; and on account of the secon- 

 dary current, for de-magnetization also. 



Experiments in electro -magnetism as a motive power, have 

 been made on a scale large enough to leave little uncertainty 

 regarding it ; governments and public bodies having, in some 

 instances, granted liberal aid to the experimentalist. Page 

 received twenty thousand dollars, or about four thousand 

 pounds sterling, towards the expenses of his experiments. 

 The most sanguine hopes of a successful result have been fre- 

 quently entertained. — Jacobi, in 1839, propelled a boat on 

 the Neva ; but he obtained only one horse-power from twenty 

 square feet of platina battery surface. Davidson, in 1842, ran 

 a locomotive, weighing five tons, on a railway near Glasgow : 

 but with a speed of only five miles an hour, which was equiva- 

 lent to one horse-power, yet he required seventy -eight pairs of 

 thirteen-inch plates of iron and amalgamated zinc. Page, in 

 1850, reported to the United States Government that he had 

 then succeeded in obtaining, at the rate of one horse-power, 

 during twenty-four hours, for twenty cents, or about tenpence 

 British ; and he stated, in a subsequent letter, that he had con- 

 structed a ten-horse engine. Nevertheless, it was announced 

 some time after, by one of his friends, that he had given up 

 the experiment, as the twenty thousand dollars, and a large sum 

 besides, had been expended on it. His engine was an ingenious 

 and powerful development of De la Rive's ring ; and when one 

 of his large helices was magnetized, three hundred pounds 

 weight of iron, which had been placed within it, was lifted up 

 by the magnetic power, and, as long as the electric current 

 was transmitted, remained suspended in the centre — realizing 

 the fabled suspension of Mahomet's coffin. Allen's electro- 

 magnetic engine w**s inspected by the presentEmperor Napoleon, 



