ELECTRIC CANDLES. 233 



centimetres per hour. As it proceeds, the points get near to the 

 supporting tubes ; but from time to time they can, without ex- 

 tinguishing the light, be restored to their original position by 

 simultaneously sliding the two carbons in the tubes. In future 

 a mechanism easy to imagine will perform this duty, and as 

 Carre makes carbons i metre long, the lamp may continue 

 lighted for twelve hours, a period longer than will ever be re- 

 quired. It will be observed that the carbons are not separated 

 by any insulating material, and that it is not necessary to point 

 them beforehand, or to fix them at their base, or to tip their ends 

 with any inflammable material. They are used as they leave 

 the manufactory. It suffices to put them into the tubes that hold 

 them, and leave them to the directing action of the exterior cir- 

 cuit. There is, in fact, no candle to be made, it is merely a 

 putting in its place of a sort of match which burns by itself to 

 the end. 



" The apparatus may be hung up in two ways, with the points 

 upwards or directed towards the ground. The conditions are 

 very different. Let us examine the first case. 



" The electric arc cannot, without breaking, exceed a length, 

 which depends on the intensity of the current. Between two 

 carbon points in a horizontal line, it should be straight, because 

 according to the laws of electric conduction, it takes the shortest 

 course and tends to return to that by virtue of a kind of elasticity 

 if withdrawn from it. But it is interfered with by the ascending 

 current of air generated by its own heat ; and for that reason 

 assumes the curved form. It is still more strongly interfered 

 with by the directive circuit (in the carbons), and these two 

 actions combine to curve it upwards until equilibrium is attained 

 between them and the elasticity (as it might be termed) of the 

 arc ; but they also cause it to become longer, they lessen its 

 resistance to rupture, and diminish the intensity of the current. 

 We see, then, that if they concur in fixing the light at the points 

 of the carbons, it is on the condition of diminishing the limit of 

 length attainable by the arc, or, what amounts to the same thing, 

 the number of arcs that a given machine will maintain. 



" It is quite a different thing when the points are turned down- 

 wards. While the arc tends to rise up along the carbons, the 

 directive circuit drives it back, and brings it down between the 

 points, which have an interval of 7 or 8 millimetres between 



