SIR WILLIAM SIEMENS, F.R.S. 259 



from the disturbing influences inseparable from a furnace worked 

 by the combustion of carbonaceous material. 



The apparatus which I employ to effect the electro-fusion of 

 such material as iron or platinum was brought before the Society 

 of Telegraph Engineers at their special meeting held on the 3rd of 

 June last, and is represented in Fig. 5, Plate 7, of the accompany- 

 ing drawings. It consists of an ordinary crucible a of plumbago 

 or other highly refractory material, placed in a metallic jacket or 

 outer casing b, the intervening space being filled up with pounded 

 charcoal or other bad conductor of heat. A hole is pierced through 

 the bottom of the crucible for the admission of a rod c of iron, 

 platinum, or such dense carbon as is used in electric illumination. 

 The cover of the crucible is also pierced for the reception of the 

 negative electrode d t by preference a cylinder of compressed 

 carbon of comparatively large dimensions. At one end of a beam 

 supported at its centre is suspended the negative electrode d by 

 means of a strip of copper, or other good conductor of electricity, 

 the other end of the beam being attached to a hollow cylinder e 

 of soft iron free to move vertically within a solenoid coil of wire/, 

 presenting a total resistance of about 50 units or ohms. By means 

 of a sliding weight g the preponderance of the beam in the 

 direction of the solenoid can be varied so as to balance the 

 magnetic force with which the hollow iron clylinder is drawn into 

 the coil. One end of the 'solenoid coil is connected with the 

 positive, and the other with the negative pole of the electric arc, 

 and, being a coil of high resistance, its attractive force on the iron 

 cylinder is proportional to the electro-motive force between the 

 two electrodes, or, in other words, to the electrical resistance of 

 the arc itself. 



The resistance of the arc was determined and fixed at wall 

 within the limits of the source of power, by sliding the weight 

 upon the beam. If the resistance of the arc should increase from 

 any cause, the current passing through the solenoid would gain in 

 strength, and the magnetic force overcoming the counteracting 

 weight, would cause the negative electrode to descend deeper into the 

 crucible ; whereas, if the resistance of the arc should fall below 

 the desired limit, the weight would drive back the iron cylinder 

 within the coils, and the length of the arc would increase, until 

 the balance between the forces engaged had been re-established. 



s 2 



