136 



UNDULATORY FORCES. LIGHT. 



[ELECTRIC LAMPS. 



hare the galvanie. batteries in any convenient place at a 

 distance from ; neuter, and to convey the elec- 



tricity, by means of the insulated wires, to the point 

 where it a wanted. Light may be obtained from the 

 battery in two ways : either by bringing the poles into 

 contact with a yard or to of platinum or indium 

 wound into the form of a spiral; or by terminating them 

 with cylinders of charcoal, and then bringing tin n 

 contact. In each ewe the light is produced oy the igni- 

 tion of the conducting medium. Platinum or indium is 

 Ki f . is?. not so well suited 



for the purpose as 

 charcoal, because, in 

 the first place, the 

 light is never so vi- 

 vid, and, in the se- 

 cond place, the metal 

 is very likely to fuse, 

 and put a stop to the 

 experiment. When 

 charcoal is employ- 

 ed, it is found that 

 the greatest inten- 

 sity of light is pro- 

 duced by drawing 

 the points apart to 

 the extent of from 

 a quarter to half an 

 inch ; and then there 

 is a stream of finely- 

 x powdered charcoal, 

 a most intensely 

 In J ignited state, pro- 

 jected from one pole 

 to the other, forming an arc of flame. If the charcoal- 

 points are too close together, 

 we do not obtain the maxi- 

 mum effect ; and if they are 

 too far apart, the arc is 

 broken, and the light extin- 

 guished. This it is which 

 constitutes the difficulty in 

 keeping up the electric light, 

 and which gives to the flame 

 its unsteady, flickering cha- 

 racter. Consequently, all the 

 contrivances which have been 

 adopted for overcoming this, 

 have been made the bases of 

 the several patents to which 

 we have alluded. These we 

 shall now proceed to describe. 

 Apparatus for sustaining 

 the Electric Light. The first 

 of Mr. Staite's patents was 

 for a contrivance or method 

 for maintaining the charcoal- 

 points at a uniform distance. 

 One of these is represented 

 in Fig. 137 : a and b are the 

 charcoal-points ; they slide 

 easily in a brass ttilxj which 

 holds them, and their free 

 ends rest upon a solid cylin- 

 der of plaster of Paris, c. At 

 the opposite ends they are 

 pressed upon by a spiral 

 spring, which is contained 

 within the brass tube ; and 

 by which means they are 

 always forced down very 

 firmly on the plaster of Paris 

 cylinder. There is an ad- 

 justing ecrew at d for regu- 

 lating the distance of the 

 points, and the arms f g con- 

 vey the current. To set it 

 in action, the two charcoal- 

 pointa are made to touch by means of the adjusting 



Fig. 139 



screw (1, and then they are separated to the required dis- 

 tance, HO as to get tin' maximum amount of light. As 

 the points burn away, the springs keep up a fresh supply 

 by furring thrin down on the plaster of Paris cylinder, 

 and maintaining them at their proper distance. It 

 was at first tin m- lit that this arrangement would meet all 

 the difficulties of the case; but it was soon found 

 that there were irregularities in the action of the 

 battery, as well as a projection of the charcoal from one 

 pole to the other, which demanded a constant motion of 

 the points ; and, therefore, a few mouths afterwards the 

 patentee adopted another invention, whereby the point* 

 were adjusted by the aid of an electro-magnet. A third 

 patent, with still further improu-incnts in this respect, 

 was obtained in the course of the same year. In this 

 last patent there are three distinct kinds of apparatus 

 nl>ed for the management of the electric light 

 namely, one for obtaining a regularly intermitting light, 

 another for procuring a constant and uniform light, and 

 a third for developing a constant light by the ignition of 

 a metallic wire. 



The apparatus for producing the first effect is repre- 

 sented in Fig. 138: a b are the two charcoal-points; 

 one of them is fixed to the conductor c, and the other 

 to the movable rod d. The lower part of d is fixed to 

 a rack/, and this to an iron rod g, which moves freely 

 up and down in a tube h, that is surrounded by a coil of 

 wire in the form of a helix : a weight i is attached to the 

 rod/o by means of a string, which passes over a pulley. 

 The object of this is to counterbalance the weight of the 

 rod, rack, and charcoal-holder ; and there is a small piece 

 of chain also attached to the weight, so that the balance 

 may be equalised as the rod is pulled down. The action 

 of the apparatus is as follows : The conductor k, and the 

 wire of the helix around h, are brought into connection 

 with the galvanic battery, and the circuit is closed by 

 bringing the two char- 

 coal-points into contact. 

 At this moment the iron 

 rod g is rendered mag- 

 netic, and is drawn down 

 into the hollow tube 

 within the helix. By 

 this means the charcoal- 

 points are separated, and 

 a most intense light is 

 produced ; but soon the 

 separation takes place 

 too far, and then the 

 circuit is broken and the 

 light extinguished. The 

 iron bar now loses its 

 magnetism, and the 

 weight draws it up 

 again, so as to bring 

 the charcoal-points once 

 more into contact, when 

 the same phenomenon is 

 repeated. It is obvious 

 that by this contrivance 

 a succession of flashes at 

 regular intervals is pro- 

 duced, and the v tight 

 may be so regulated as 

 to maintain any period 

 for the duration of the 

 light and its intermis- 

 sion. 



The apparatus for pro- 

 dncing a constant and 

 uniform light is shown 

 in Fig. 139. The char- 

 coal-points A B are at- 

 tached as before one 

 to a fixed conductor C, 

 and the other to a move- 

 able conductor D ; the 

 latter is moved by a 

 rack F F, wliich works into a pinion, and this turns on 



