72 Royal Society: — Mr. Tisley on a new 



1867 (see Eoyal Society's Transactions) the power of augmenting 

 the magnetism by successive currents, developed from the original 

 residual magnetism contained in the iron, was fully demonstrated, 

 and it was shown that the power of the machine could thereby 

 be developed to a great extent ; but the only means for obtaining 

 external work was by the insertion in the circuit of a magnet or 

 coil so that the secondary discharge could be utilized. Sir Charles 

 Wheatstone also showed that a great part of the current could 

 be shunted through a platinum wire, care being taken that the 

 resistance of the platinum wire was sufficient to compel a large 

 part of the current to pass round the electromagnet. 



In the same year the writer designed a machine which was made 

 by Mr. Ladd, and described by him in a paper read before this 

 Society (see Transactions), the principle of which was that two 

 separate armatures being introduced, one was employed for mag- 

 netizing the machine, the other being used for external work. 

 This machine gave a good electric light &c, and was shown in 

 the Exhibition of Paris, 1867, when a silver medal was awarded 

 for it. 



To simplify this machine, the author of this paper afterwards 

 placed the two armatures in the same groove between the poles 

 of the electromagnet, bolting the two together at right angles to 

 each other, so that they came under the influence of the magnetism 

 alternately; by this method one pair of bearings was sufficient 

 instead of two, and the machine altogether was much simplified. 



The machiue now about to be described is a still further modifi- 

 cation, in which the greatest amount of simplicity and effective 

 power are combined. 



The apparatus consists essentially of an electromagnet with 

 shoes, forming a groove in which a Siemens's armature is made to 

 revolve: this is much the same as the original machines made by 

 Siemens and Wheatstone ; but the difference occurs in the break or 

 commutator ; here there are two springs or rubbers employed in 

 taking the current off from the commutator. The commutator con- 

 sists of three rings : one of these rings is complete for three quarters 

 of the circle, the other quarter being cut away ; another ring is cut 

 away three quarters, leaving the one quarter ; and in between these 

 two rings is a third ring, insulated and connected with the insu- 

 lated end of the wire wound round the armature ; on this centre 

 ring are projecting pieces, one a quarter of a circle and the other 

 three quarters, so arranged as to complete the two outer circles. 

 The rubber spring which comes into contact with the quarter of 

 the middle circle is connected with the electromagnet of the machine, 

 and the armature is so arranged that at the time of contact the 

 best magnetizing current is developed. The other spring rubber 

 is in connexion Math the wire on the armature during the other 

 three quarters of its revolution ; and this is connected with any 

 external piece of apparatus required to be worked. 



By this arrangement, the alternate currents being utilized, they 

 are all in the same direction; and by the length of contact the 



