ELECTRIC LAMPS. ] 



UNDULATORY FORCES. LIGHT. 



137 



a spindle with fixed supports. A barrel is attached to 

 the pinion, and over this there passes a string, to which 

 the weight G is fastened: by this means the rod and 

 rack D F are counterpoised. To the spindle there is fixed 

 a cogged wheel H and a lever I; the latter carries a 

 double paul, which locks into the cogs of the wheel in 

 either direction. A long horizontal lever, K, passes 

 over the paul, and moves on the fulcrum L ; while it 

 supports at one end a rod M, which is fixed to an iron 

 bar N, and at the other a movable counterpoise O. The 

 iron bar travels freely up and down in the coil P. 



The paul and its lever I are kept in a state of slow 

 vibration from side to side by means of a crank R, which 

 works in a fork at the end of the lever I. This crank is 

 made to revolve by an ordinary train of wheelwork, 

 furnished with an escapement or fly-wheel, and driven 

 by spring-power or by weights. The object of tliis 

 movement is to elevate or depress the rack F by turning 

 the wheel H. 



The mode of action of the apparatus is as follows : 

 The negative pole of the battery is brought into contact 

 with the rack and rod D, F, and the positive pole with 

 the coil P, and thence with the upper charcoal support 

 C. Immediately the points touch, and the circuit is 

 completed, the coil raises the iron rod N. This acts on 

 the lever K, and causes the lower charcoal-point to 

 descend and separate from the upper one. Directly the 

 separation has taken place to the maximum extent, there 

 is a contrivance (not shown in the drawing) which arrests 

 thi movement of the rack, and no keeps the electrodes 

 stationary. Before the apparatus is set to work, the 

 proper distance for the charcoal-points is adjusted by 

 means of the counterpoise O, which screws backwards or 

 forwards on the short arm of the lever K, and thus 

 regulates the movement of the rod M, N. If the light 

 should go out, and the circuit be broken, the rod N im- 

 mediately falls, pulling down with it the long end of the 

 lever K. This presses upon one arm of the paul, and 

 gives motion to the wheel H, whereby the rack is 

 elevated, and the charcoal-points again brought into 

 contact. 



M. Lemolt's apparatus for adjusting the charcoal 

 electrodes is somewhat different from the last. In the 

 first place, the electrodes are not cylindrical, but are in 

 the form of circular discs, o, 6, Fig. 140; and they re- 



reive freely on two arms, which move separately on one 

 common axis, c. This axis also carries a pinion, the 



VOL. I. 



square cogs of which are in communication below with 

 the driving-wheel d, and above with another pinion /, 

 the inner cogs of which are in gear with a large wheel g. 

 Over the drum of the pinion at c, there pass two endless 

 pulleys, which give motion to the charcoal discs, a, b. 

 In order that the discs may be at a proper distance for 

 the production of a good light, there are two adjusting 

 stops h h, fixed to the arms on which the discs rotate. 

 These stops are brought into close contact with two 

 cams, which are situated in the periphery of the wheel 

 g ; and as this wheel rotates, the charcoal discs are 

 brought closer and closer together, so as to compensate 

 for the wear of the electrodes. There is a spiral spring 

 at i to keep the anus and their stops tight against the 

 cams. The apparatus is thus set in motion the termi- 

 nal wires of the battery are brought into connection with 

 the charcoal discs by means of the conductors k, I. The 

 driving-wheel <i is then set in motion by clockwork 

 within the case of the instrument, and its motion is com- 

 municated to the other wheels, and also to the charcoal 

 discs. The discs are then brought together so as to 

 complete the circuit, and the stops are adjusted in the 

 cams, so as to produce the necessary arc of flame. By 

 the revolution of the discs, new surfaces are constantly 

 presented to each other, and the old or worn edges are 

 cleaned down by the sides of the stirrups in which they 

 revolve. 



In Mr. Pearce's arrangement, there is a prismatic or 

 cylindrical bar-electrode in contact with one, two, or 

 three of a discoid form. These are moved by clock- 

 work ; and it is so managed, that while the first advances 

 or rises through its sheath, the others revolve at a pro- 

 per distance from it, and the edges are kept clean by 

 means of indium cutters. The charcoal bar is also held 

 by the indium conductors, which grasp it close to the 

 ignited point. The advantage of this mode of mounting 

 the electrodes is, that if from any cause, such as un- 

 equal waste of carbon, or irregularity of surface, the 

 light should be extinguished at one point, the others re- 

 main burning, until by the further revolution of the 

 disc, or the advance of the bar, the electrodes are again 

 brought into contact, and the light restored. Besides 

 which, in presenting two or three centres of light, so 

 merged as to appear as one in a reflector, there is greater 

 brilliancy and greater steadiness of flame. 



Another apparatus has been patented by Mr. Pearcc, 

 which does away with the necessity of clockwork alto- 

 gether. It consists of two bar-electrodes, which are 

 approximated by means of springs or weights and 

 pulleys ; and the necessary distance is preserved by the 

 intervention of slips of non-conducting charcoal. He 

 has also contrived a plan for relighting the electrodes in 

 case the arc of flame is blown out. This he effects by 

 aid of a wedge-shaped piece of charcoal, which falls down 

 between the electrodes directly the light is extinguished, 

 and thus re-establishes the contact. The charcoal is 

 fixed at one end of a lever, and to the other end there is 

 a soft iron armature : this is placed opposite to a soft 

 iron magnet, enclosed in a coil which carries the current. 

 \Vhile the electricity is passing, the electro-magnet draws 

 the armature to it, and so keeps the wedge-shaped piecu 

 away from the electrodes ; but directly contact is broken, 

 the armature retires, and the wedge-shaped piece falls 

 down between the poles and re-establishes the arc. 



Mr. Staite has patented a plan for obtaining a constant 

 and uniform light by the ignition of a loop of platinum 

 or indium wire, enclosed in a glass globe from which the 

 air has been exhausted. But there is no novelty 

 whatever in ihis contrivance ; and, consequently, it is 

 undeserving of further notice. 



Some little attention is necessary to the quality of the 

 electrodes, in order to get the best effect. Common 

 charcoal is unsuited for the purpose, because of its being 

 n most cases a non-conductor of electricity ; the charcoal 

 of porout wood is also objectionable, from the circum- 

 stance of its burning away very rapidly : therefore it is 

 ,hat electricians make choice of the densest varieties of 

 carbon. One of these is the charcoal from boxwood, 

 which is obtained by cutting the wood into pieces of 



