242 SEC. 9. MAGNETISM. 



1123. Proment's Engine. AU electro-magnetic machine 

 depending upon the successive attraction by fixed electro-magnets 

 of bars of soft iron fastened on a wheel and parallel to its axis. 



Frederick Guthrie, F.R.S. 



The successive magnetization and demagnetization of the magnets is 

 effected by the action of cams on the axis of the wheel, which lift ivorj 

 rollers, and so displace springs to which they are fastened. 



1124. Helmholtz's Electro-magnetic Engine. 



F. Rob. Voss, Berlin. 



The advantage of this machine is that it is set in motion by a very small 

 galvanic force; with two Bunsen elements it will drive one of Professor 

 Helmholtz's double-syrens or one of his centrifugal commutators. 



Professor Helmholtz has applied a contact-arrangement to the commutator 

 of the Siemens' bobbin, which surpasses all former ones in that it avoids great 

 surfaces of friction, and so greater power and speed is attained. 



This is a new instrument, and consists of an insulated plate covered with 

 tinfoil, on which is screwed a metal ring, inside this a glass ball runs about ; 

 one pole of an electric machine is in contact with the tinfoil, and the other 

 pole with the metal ring ; when the current passes the ball runs about, 



1124a. Electro-magnetic Machine, with velocity regu- 

 lator. Helmholtz. 



Physical Institution of Berlin, Prof. Helmholtz. 



The current which drives the electro-magnetic machine is interrupted 

 by the centrifugal regulator whenever the velocity exceeds a certain limit, 

 whereupon the driving force ceases. Using a current which is only a little 

 stronger than what exactly suffices for the normal velocity, exceedingly 

 constant velocities of rotation are obtained. (Described by M. Exner in the 

 Litzungsberichte of the Vienna Academy, Math. Natura. section, Bd. LVIIL, 

 Abth. II., page 602.) 



1125. Electro-magnetic Engine. F. Stohrer, Leipzig. 



1125a. Electric Motive Power, acting on a pump 



M. Loiseau, junior, Paris. 



1125b. Electric Motive Power, acting on a jet of water. 



M. Loiseau, junior, Paris. 



1125c. Electric Motive Power, acting upon a hammer. 



M. Loiseau, junior, Paris. 



1125d. Electric Lighting Apparatus. 



M. Loiseau, junior, Paris. 



1125e. Electric Telegraph. M. Loiseau, junior, Paris. 



1 125f. Electro-Magnetic Machine, invented by Sir" Charles 

 Wheats tone. 



Wheatstone Collection of Physical Apparatus, King's 

 College, London. 



