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X. Intelligence and Miscellaneous Articles. 



ON THE ELECTRIC LIGHT. BY J. JAMIN. 

 F HAVE the honour to present to the Academy a pattern of elec- 

 -*- trie burner reduced to the simplest form possible. The two car- 

 bons are maintained parallel by two insulated copper tubes separated 

 by an interval of 2 or 3 millims., in which they slide with friction, 

 and which serve at the same time to direct them and to bring the 

 current. They are surrounded by a directing circuit composed of 

 five or six helices coiled upon a thin rectangular frame 40 centims. 

 in leugth and 15 centims. wide. I have explained how this circuit, 

 traversed by the same current as the carbons and in the same 

 direction, brings and fixes the electric arc at the extremity of the 

 points. 



The lighting takes place automatically. For this purpose the 

 two extremities of the carbons are wrapped round with a thin 

 caoutchouc band, which presses them to one another ; a small piece 

 of iron wire is then insinuated between them, or a little above, 

 which puts them into communication at one point only. As soon 

 as the circuit is closed the current passes through this wire, makes 

 it red-hot, and melts the caoutchouc; the two carbons, having 

 again become free, separate, aud the arc is set up with a sort of 

 explosion. Carbons can be employed of any size up to 8 milliuis. 

 diameter. At this limit the wear does not exceed 8 centims. per 

 hour. As it goes on, the points approach the supporting tubes ; 

 but they can be from time to time brought back to their initial po- 

 sition by sliding the carbons in the tubes by a common movement, 

 without extinguishing them. In future applications an easily de- 

 vised mechanism will perform this office ; and as M. Carre manu- 

 factures carbons the length of which reaches 1 metre, the lamp can 

 remain lighted during twelve hours, which exceeds all needs. It 

 will be remarked that the carbons are not separated by any insula- 

 ting material, that it is not necessary to first break off their points, 

 nor to fix them at their base, nor to furnish them at their point 

 with any inflammable material ; they are used just as they come 

 from the maker's. It is sufficient to introduce them into the tubes 

 which are to support them, and to leave them to the directing action 

 of the outer circuit. In reality there is no candle to construct ; there 

 is only a sort of wick to place, which burns all alone to the end. 



The apparatus can be suspended in two ways — either with the 

 points above, or directing them towards the ground. These are 

 very different conditions. Let us study the first case. 



The electric arc cannot, without breaking, exceed a length de- 

 pending on the intensity of the current. Between two horizontal 

 points it should be rectilineal, because, according to the laws of 

 conductivity it takes the shortest path, and tends to return to it 

 when forced to deviate, in virtue of a sort of elasticity. But it is 

 deranged by the ascending currents of air occasioned by its heat ; 

 and that is why it takes a curved form. It is also deranged, and 

 much more energetically, by the directing circuit. These two ac- 

 tions join in bending it upwards until equilibrium is established 

 between them and its elasticity ; but they also combine to lengthen 



Phil Mag. S. 5. Vol. 8. No. 46. July 1879. G 



