VOLTAIC ARC LAMPS. 193 



jointed arms of which carry at their ends the carbon-holders, 

 which are therefore horizontally opposite to each other. 

 These two arms of the compass are insulated from each 

 other and are very readily movable. They are connected 

 with the two branches of the circuit, and when the carbons 

 come into contact by the tendency of the carbon-holders to 

 place themselves vertically, the passage of the current which 

 then takes place produces a repulsion that separates the 

 carbons and produces the arc. There is then established a 

 state of equilibrium between this repulsive force and that 

 due to gravity. This state of equilibrium is sufficiently 

 stable to render the arc comparatively steady. But this 

 system can be used only with currents of small intensity, and 

 it cannot be considered of any practical use. The same 

 may. be said of that of Fernet, which is arranged according 

 to the same principle. 



In conclusion, we shall mention a lamp invented by Dubos, 

 which is rather interesting from its arrangement. 



In this lamp the luminous point remains fixed without any 

 clockwork, in consequence of the shape of the two carbons, 

 which are semicircular. These carbons are supported by 

 two arms jointed to a pivot in the centre of the circumfer- 

 ence formed by the two carbons. As in the ordinary regu- 

 lators, an electro-magnetic mechanism fixed to the carbon- 

 holders brings them together as they are consumed. As 

 these displacements take place circularly, the point of 

 contact of the two remains always at the same height, 

 and consequently the same is the case with the luminous 

 point. 



There are yet a few other lamps which were shown at the 

 Exhibition at the Albert Hall, and which have been described 

 in various works, in those of Fontaine and Higs, among the 

 rest ; but these lamps are merely more or less complicated 

 modifications of those we have described, and therefore we 

 shall here merely make a note of them. Of these, we shall 



