368 Conversion of Bynamical into Electrical Force. [Feb. 14_, 



not requisite in order to convert mechanical into electrical force ; and the 

 result obtained by this experiment is remarkable, not only because it de- 

 monstrates this hitherto unrecognized fact, but also because it provides a 

 simple means of producing very powerful electrical effects. 



The apparatus employed in this experiment is an electro-magnetic machine 

 consisting of one or more horseshoes of soft iron surrounded with insulated 

 wire in the usual manner, of a rotating keeper of soft iron surrounded 

 also with an insulated wire, and of a commutator connecting the respective 

 coils in the manner of a magneto -electrical machine. If a galvanic battery 

 were connected with this arrangement, rotation of the keeper in a given 

 direction would ensue. If the battery were excluded from the circuit and 

 rotation imparted to the keeper in the opposite direction to that resulting 

 from the galvanic current, there would be no electrical effect produced, 

 supposing the electro-magnets were absolutely free of magnetism ; but by 

 inserting a battery of a single cell in the circuit, a certain magnetic condition 

 would be set up, causing similar electro-magnetic poles to be forcibly ap- 

 proached to each other, and dissimilar poles to be forcibly severed, alter- 

 nately, the rotation being contrary in direction to that which would be pro- 

 duced by the exciting current. 



Each forcible approach of similar poles must augment the magnetic ten- 

 sion and increase consequently the power of the circulating current ; the 

 resistance of the keeper to the rotation must also increase at every step 

 until it reaches a maximum, imposed by the available force and the Qon- 

 ductivity of the wires employed. 



The cooperation of the battery is only necessary for a moment of time 

 after the rotation has commenced, in order to introduce the magnetic action, 

 which will thereupon continue to accumulate without its aid. 



AVith the rotation the current ceases ; and if, upon restarting the machine, 

 the battery is connected with the circuit for a moment of time with its 

 poles reversed, then the direction of the continuous current produced by 

 the machine will also be the reverse of what it was before. 



Instead of employing a battery to commence the accumulative action of 

 the machine, it suffices to touch the soft iron bars employed with a perma- 

 nent magnet, or to dip the former into a position parallel to the magnetic 

 axis of the earth, in order to produce the same plienomenon as before. 

 Practically it is not even necessary to give any external impulse upon re- 

 starting the machine, the residuary magnetism of the electro-magnetic 

 arrangements employed being found sufficient for that purpose. 



The mechanical arrangement best suited for the production of these cur- 

 rents is that originally proposed by Dr. Werner Siemens in 1857* consist- 

 ing of a cylindrical keeper hollowed at two sides for the reception of insu- 

 lated wire wound longitudinally, which is made to rotate between the poles 

 of a series of permanent magnets, which latter are at present replaced by 



* See Du MoRcel ' Sur rElectricite,' 1862, page 248. 



