UND0LATORY FORCES. ELECTRO-MAGNETISM. [BMCTKO-MAOHCTIC BKOWM. 



greater linear or radiating influence from ito source, a 

 good and useful engine, driven by electricity, will remain 

 to be Bought after. 



Having stated thews difficulties, we will now describe 

 some of the engines which tin- sanguine but disappointed 

 in yen tor* hare patented, and brought more or leu* into 

 pub lie notice. In doing so, we shall not ]. ay Any heed 

 to their chronological onler, but rather to that of the 

 principles on which they are constructed. \\ r o may 

 divido them into two olasses-namoly, those, 1st, in which 

 the motion is as a tangent in its direction to the lines of 

 force ; and, 2nd, such as, like the ordinary power of the 

 steam-engine, have a reciprocating motion. Thoro are 

 other forms, to which wo shall also allude in general 

 terms, which daim attention rather for their ingenuity 

 than their value. 



Those machines in which motion is obtained in a ta 

 gcntiiU arrangement of permanent and electro-magnets, 

 hare been of numerous forms, according to the ideas of 

 their inventors. The permanent magnets are always 

 stationary ; and the electro-magnets are made to revolve 

 so that their poles may be nearly in contact with those 



of the former kind. 

 The annexed engraving 

 gives a view, in section, 

 of this kind of machine, 

 and shows the relative 

 position of each kind 

 of magnets. The less 

 important parts aro 

 omitted, as is also the 

 arrangement, by means 

 of which contact is 

 broken between the 

 electro-magnets and the battery ; for such varies so 

 much in form, whilst the principle is the same in 

 every instance. 



In the above figure, a, a are two permanent and com- 

 pound horse-shoe magnets,* which are fixed on a wooden 

 foot; 6 6 b b are the four terminals, or poles, of as 

 many electro-magnets, made in the usual manner. The 

 wires of the ends of each electro-magnet are attached to 

 a suitable arrangement, by means of which a current 

 of electricity from a few cells of a voltaic battery is 

 conveyed by them. As each pole of the electro-magnets 

 approaches those of the permanent magnet, the current 

 of electricity, producing magnetism in the soft iron, causes 

 a powerful attraction. As the pole passes a little beyond 

 the centre of the permanent magnet, the supply of elec- 

 tricity is cut off, and the soft iron thus returns to its 

 normal state. Of course, the same happens to each 

 electro-magnet as it approaches either of the permanent 

 magnets, and thus a rapid revolution is produced. Very 

 little power is afforded by this arrangement, which may 

 be taken as a type of its class. In some of these 

 machines a permanent magnet is placed, so as to be 

 opposite each electro-magnet one during each revolu- 

 tion ; and the number of both may bo increased to any 

 extent. These nifty be arranged to revolve on their 

 axis (c, in Fig. 13) as often as from 300 to 500 times per 

 minute ; but owing to the attractive force diminishing 

 in so rapid a ratio as each magnet passes on, the motion 

 of the machine may bo stopped by the slightest obstacle 

 applied to the arms of the electro-magneto. When 

 machines of this kind are constructed on the largo 

 scale, and used for driving lathes, A-c., the speed of the 

 driving-wheel, or that which communicates its motion 

 to the machinery, is diminished below that of th< 

 electro-magneto by the interposition of variously sizec 

 cog-wheels. 



The next form of electro-magnet to which wo shal 

 direct attention, is that wherein a crank is employed, 

 which is moved by moans of levers placed over the 

 electro-magnet, and attached, at their other extn-< 

 to a fulcrum. These machines aro generally 

 with two sets of electro-magneto, &c., and the cranks 

 are placed at right angles to each other on the crank 

 shaft ; so that when one is on the dead points, the other 



Sec antf, p. 211. 



may be in full action. This form of machine, liko that 

 winch wo Lint described, has been the subject of nume- 



rous modifications : Fif . u. 



its type, however, 

 is illustrated in the 

 annexed engrav- 

 ing. In Fig. 14, 

 the general ar- 

 rangement will IT 

 eon of one side 

 of those machine* : 

 a is the electro- 

 niagnet ; 6 is a soft 

 iron keeper, at- 

 tached to the lever 

 c this having a 

 ulcrum at d. The 

 ever is attached to 

 ho crank at c, which is again fixed on an axle of the 

 fly-wheel, g, at /. The other cranks, <vc., are not 

 shown, so as to avoid confusion of detail. When a 

 current of electricity passes round either electro-magnet, 

 ,ho attraction induced draws down the keeper, and so, 

 >y means of the lever, produces a rotary motion through 

 the crank fixed on the shaft. As one keeper rises, the 

 other one falls, and thus the general action resembles 

 that of a double-cranked, <tc., steam-engine. The con- 

 act between the electro-magnet and the battery is 

 irokcn by means of any form of contact-breaker, at- 

 ached either to the crank or lever. By means of this 

 form of machine, a greater amount of power is obtained 

 tlian that produced by the one wo last described ; but 

 still the result, in an engineering point of view, is com- 

 paratively trifling. An effective modification of this 

 kind of electro-magnetic engine the invention of M. 

 Fromcnt, of Paris is represented in the following en- 

 graving. 



Fig. 15. 



It will bo impossible for us to describe the various 

 arrangements which have been proposed by numerous 

 inventors. M. Jacobi, of St. Petersburg, Messrs. Joule, 

 Sturgeon, Davenport, Davidson, and many of the lead- 

 ing electricians and philosophical instrument-makers of 

 this and other countries, have applied an inim- 

 amount of theoretical and practical knowledge to the 

 subject. One of the best arrangements wo have seen, is 

 that invented by Mr. Allan, of the Adclphi, London ; 

 who has devoted himself, with great ardour and success, 

 to the pursuit of every branch of electrical science. He 

 employs a number of circular plates, pl.-i.-.-d over as 

 many electro-magnets. Through each of these plates a 

 rod runs ; at the lower part of which is a pivot. The 

 upper end of the rod U connected to a crank ; and a set 

 of plates and electro-magneto aro placed vertically over 



