270 



ELECTRIC LIGHT. 



of uniform texture conditions that produce a 

 fluctuating and unsteady light and the forma- 

 tion of sparks ; the pencils are also liable to 

 split, and portions become detached under the 

 action of the high heat to which they are sub- 

 jected. 



To obtain perfectly homogeneous carbons va- 

 rious artificial processes have been suggested, 

 among which two, both of them French inven- 

 tions, have yielded very fair results. In one of 

 these processes devised by M. Carr6, a composi- 

 tion consisting of powdered coke, calcined lamp- 

 black, and a sirup made of twelve parts gum 

 and thirty of cane-sugar, is employed. This 

 mixture is thoroughly ground together, water 

 added to form a paste of the desired consist- 

 ency, and the mass then pressed through a die- 

 plate by which the proper form is given to the 

 carbons. These are afterward packed in cru- 

 cibles and subjected to a high temperature for 

 several hours, then removed and soaked in a 

 boiling sirup to fill up the pores, and after 

 draining subjected to another baking. These 

 operations are repeated with various modifica- 

 tions until the carbons have acquired the neces- 

 sary hardness and solidity. In use they are 

 said to be much superior to the ordinary re- 

 tort carbons ; but they have their defects 

 nevertheless, the most serious of which are 

 a rapid wasting away, and considerable ir- 

 regularity of luminous effect. The carbons 

 that so far have given most satisfaction are 

 made after a process invented by M. Gau- 

 doin. The first step in this process has for its 

 object the production of a pure form of carbon 

 which the inventor obtains by the decomposi- 

 tion in closed vessels of the dried pitches, fats, 

 tars, resins, bitumens, essences, oils, and other 

 organic matter. The carbon thus derived is 

 pulverized as finely as possible, and then ag- 

 glomerated either alone or with a certain quan- 

 tity of lampblack by means of the carbides of 

 hydrogen obtained as secondary products. The 

 material is then molded under heavy pres- 

 sure into the form required for use. These 

 carbons are consumed more rapidly than the 

 retort carbons, but less so than those produced 

 by the Carre" process, and in all other impor- 

 tant respects, such as the power, brilliancy, 

 and steadiness of the light, absence of sparks, 

 tenacity and even consumption of the pencils, 

 they leave little to be desired. 



As the carbons, whatever their make or how- 

 ever well they are protected, slowly waste away 

 when the light is in operation, it becomes ne- 

 cessary to move them together at a rate pro- 

 portioned to the rapidity with which they are 

 consumed. If the light is to be continuous, the 

 distance between the carbon points must be 

 kept constant; and, as the positive carbon is 

 destroyed much faster than the negative car- 

 bon, provision must be made for a correspond- 

 ing increase in its velocity. To maintain this 

 adjustment of the carbon points has always 

 been one of the chief difficulties in the way of 

 electric illumination, and a large number of in- 



ventions, some of them simple and others ex- 

 ceedingly complex, have been offered for the 

 purpose and used with varying degrees of suc- 

 cess. The later devices show a marked tendency 

 toward greater simplicity of structure and a 

 corresponding increase in efficiency. The ap- 

 paratus for carrying the carbons, combined with 

 the mechanism required for their continued ad- 

 justment, is called the electric lamp. It is usu- 

 ally so arranged that the carbons are held in a 

 vertical position, and by means of the regulators 

 the light is kept at a nearly uniform level. One 

 of the earliest forms of such a lamp is shown in 

 Fig. 1. It was invented by M. Foucault, and af- 

 fords a fair idea of the complexity of the mech- 

 anism employed in the electric lamp to regulate 

 the movements of the carbons. In this apparatus 

 there are two systems of automatic wheel-work, 

 one for bringing the carbon points together when 

 it is wished to start the light, and the other for 

 separating and maintaining them in the proper 

 relation for the continuation of the light. 



L' is a barrel driven by a spring inclosed 

 within it, and driving several intermediate 

 wheels, which transmit its motion to fly o. L is 

 the second barrel, driven by a stronger spring, 

 and driving in like manner the fly o'. The racks 

 which carry the carbons work with toothed 

 wheels attached to the barrel L', the wheel for 

 the positive carbon having double the diame- 

 ter of the other, the same as in the Duboscq 

 lamp. The current enters at the binding screw 

 C, on the base of the apparatus, traverses the 

 coil of the electro- magnet E, and passes through 

 the wheel-work to the rack D, which carries 

 the positive carbon. From the positive carbon 

 it passes through the voltaic arc to the negative 

 carbon, and thence, through the support H, to 

 the binding screw connected wilh the negative 

 pole of the battery. When the armature F 

 descends toward the magnet, the other arm of 

 the lever F P is raised, and this movement is 

 resisted by the spiral spring R, which, however, 

 is not attached to the lever in question, but to 

 the end of another lever, pressing on its upper 

 side and movable about the point X. The low- 

 er side of this lever is curved, so that its point 

 of contact with the first lever changes, giving 

 the spring greater or less leverage, according 

 to the strength of the current. In virtue of 

 this arrangement, the armature, instead of be- 

 ing placed in one or the other of two positions, 

 as in the ordinary forms of apparatus, has its 

 position accurately regulated, according to the 

 strength of the current. The anchor T t is 

 rigidly connected with the lever F P, and fol- 

 lows its oscillations. If the current becomes 

 too weak, the head t moves to the right, stops 

 the fly o' and releases 0, which accordingly re- 

 volves, and the carbons are moved forward. If 

 the current becomes too strong, o is stopped, o' 

 is released, and the carbons are drawn back. 

 When the anchor T t is exactly vertical, both 

 flies are arrested, and the carbons remain sta- 

 tionary. The curvature of the lever on which 

 the spring acts being very slight, the oscilla- 



