544 Royal Society : — ] 



tain itself, as in the Ruhmkorff's coils. (This current is called 

 by foreigners the extra-current.) 



The shunt which Wheatstone inserted carries this current across, 

 and so maintains the magnetism of the electromagnets until the arma- 

 ture gives a second impulse. The current in this shunt will be found 

 to travel in alternate directions ; not so that on the electromagnet. 



"When the armature is discharging its current into the electro- 

 magnets, the current in the shunt is in the direction it would have 

 if the shunt were in circuit solely with the armature. 



"When the armature is changing poles and is disconnected, the se- 

 condary current is in full play, and the current in the shunt is in the 

 direction of the current prolonged in the electromagnet, that is, of 

 the extra current. 



The force expended in the shunt is wasted in heat ; but a secondary 

 wire on the electromagnet or a copper cylinder would very greatly 

 add to the power by maintaining the magnetism, and not consume 

 uselessly the force now wasted in the shunt. 



The overlapping of the armature and the solid mass of the elec- 

 tromagnets tends to maintain imperfectly the magnetism during the 

 intervals of no current from the armature ; and but for this the ma- 

 chines, whether they be Wilde's, Wheatstone' s, or Siemens' s, would 

 none of them work. 



In 1860 I published a description of two machines I had con- 

 structed, and in 1862, at the Universal Exhibition, I exhibited a ma- 

 chine for adding mechanical force to static electricity without fric- 

 tion. A machine similar in principle, but a little different in construc- 

 tion, has been exhibited recently under the name of Holtz. 



One of my machines bears to the other precisely the same relation 

 that Siemens's or Wheatstone's does to Wilde's. 



If these be of sufficient interest to the Royal Society, I shall be 

 happy to exhibit them. 



I am, my dear Sir, 



Very truly yours, 



C. F. Varley. 



« On a Magneto-electric Machine." By William Ladd, F.R.M.S. 



In June 1864 I received from Mr. Wilde a small magneto-electric 

 machine, consisting of a Siemens's armature and six magnets. This 

 I endeavoured to improve upon, my object being to get a cheap ma- 

 chine for blasting with Abel's fusees. This was done by making one 

 of circular magnets, and a Siemens's armature revolving directly be- 

 tween the poles, the armature forming the circles ; with this I could 

 send a very considerable power into an electro-magnet, &c. It was 

 then suggested to me by my assistant, that if the armature had two 

 wires instead of one, the current from one being sent through a wire 

 surrounding the magnets, their power would be augmented, and a 

 considerable current might be obtained from the other wire available 

 for external work ; or there might be two armatures, one to exalt the 

 power of the magnets, and the other made available for blasting or 

 other purposes. Want of time prevented me carrying this out 



