LUMINOUS EFFECTS.] 



UNDULATORT FORCES. ELECTRICITY. 



191 



In all the batteries we have described, the effects pro- 

 duced have resulted from the decomposition of water. 

 Professor Grove, however, has constructed a gas battery, 

 in which the combination of .oxygen with hydrogen, and 

 the consequent production of water, is sufficient to 

 afford a current of electricity. One of these arrange- 

 ments is represented in the following engraving (Fig. 47) ; 

 in which each glass contains two tubes, one filled with 

 hydrogen, and one with oxygen. A platina plate is 

 soldered so as to expose its surface to the gas inside the 

 glass. A wire passes from each tube ; and the oxygen of 

 one glass tube is thereby connected to the hydrogen of 

 the next, and BO on. A wire is brought from the two 

 end-tubes of the series, by means of which the current of 

 electricity is guided to any desired place. The tubes are 

 filled with the gases, in the same proportions, by bulk, as 

 are required to form water; and during the action of 

 the battery, they diminish through their conversion into 

 water. The liquid, which should be dilute sulphuric 

 acid, in each glass vessel, rises, for the same reason, in 

 the tubes. By means of this arrangement, all the 

 ordinary effects of the voltaic battery are readily ob- 

 tained. Fig. 47 represents one of these singular ar- 

 rangements. 



Fig. 47. 



Having thus described the leading forms of voltaic 

 batteries, we shall pass on to examine the various effects 

 which may be produced by them. 



THE LUMINOUS EFFECTS OF VOLTAIC 

 BATTERIES. 



IN the whole range of experimental science, we can find 

 no results of so brilliant a kind as those produced by a 

 powerful voltaic battery. It will be necessary to have 

 at least twenty of either Daniell's, or forty of Smee's 

 arrangements, to repeat the experiments we shall name. 

 To those who can afford larger apparatus, we may 

 mention, that forty cells of Grove s battery, having 

 platinas six inches long and two inches wide, afford 

 some splendid effects ; but, for general use, we recom- 

 mend the simple modification of Grove's, which we fully 

 described in a previous page,* and which will answer 

 every purpose. In all the following experiments, each 

 part of the apparatus and wires, and all the connections, 

 should be kept perfectly clean and polished by a con- 

 stant and liberal use of sand-paper ; and some fine 

 copper wire is useful to tie and connect metallic points, 

 Ac. The student should provide himself with such a 

 stand as we described in our remarks on frictional elec- 

 tricity^ or he may easily construct one out of a piece of 

 mahogany ; and on this, two uprights should be placed, 

 so as to support two crayon -holders, in which charcoal 

 Fig. . , 







and other points can be held. Oil" nf thue arrange- 

 ments is represented in the above engraving. 



In Fig. 48, a is the table of the apparatus ; 6 b, _. , 



S mil, f. 189. t See ante, p. 182 ; Fig. 30. ) See ante, p. 100. 



the two uprights ; c c the crayon-holders ; d d the char- 

 coal, or other points; e the arc of light; z the wire 

 from the zinc ; and p, the wire from the platina of the 

 battery. With such an instrument, the following ex- 

 periments may be tried. 



Experiment 34. Insert in each crayon-holder a piece 

 of pointed boxwood charcoal, or of the hard carbon 

 formed inside gas-retorts ; and having attached the wires 

 of the battery to the crayon-holders, bring the two 

 charcoal points into contact. They will immediately 

 become red-hot ; and if they be separated for a short 

 distance, a brilliant arc of flame will extend between the 

 points. This light, which, par excellence, is called the 

 Electric Light, far exceeds, in intensity, any other kind of 

 artificial light we can obtain. It is not due to com- 

 bustion, for it will take place equally well beneath the 

 surface of water, or even in the vacuum of an air-pump. 

 It is due to the fact that fine particles of carbon are 

 transferred rapidly from one pole to the other. This is 

 easilv noticed when a powerful battery is employed ; for 

 one point gradually increases iu size, whilst the other 

 becomes perforated with holes. 



We have already given some account of the effects to 

 be obtained by using powerful batteries, at a previous 

 page ;t but we may remark, that a light produced 

 by fifty cells of a Grove's battery, with platinas four 

 inches long and two wide, is equal to about 1,000 

 wax candles, of six to the pound, all burning at the 

 same time. 



The objections to the use of this light, are its great 

 unsteadiness, and the intensely black shadow wliich it 

 casts. The latter difficulty cannot be overcome ; and 

 every attempt has been made to compensate for the 

 irregularity and intermittence which occurs, by the con- 

 struction of electric lamps, some of which have already 

 been illustrated in our chapter on artificial illumination. 

 We have tried some of the best lamps yet constructed by 

 the most celebrated makers, and others which we have 

 had made ourselves ; and we cannot but unhesitatingly 

 observe, that they are all failures in every respect. The 

 objection of expense in of no great force, because the 

 intensity of the light is so great. 



The application of the electric light to lighthouse 

 purposes, has, however, been highly successful ; and for 

 many months, the South Foreland shone brilliantly with 

 the light produced by the magneto-electric machine, 

 which we shall describe under the head of Electro- 

 Magnetism. At the present time, some parts of Paris 

 are thus lit, and the effect is stated to be very line. The 

 electric light seems to have what we may call a space- 

 penetrating power, and it can accordingly be seen 

 further in a fog than any other kind of artificial light ; 

 its value for lighthouses, on this ground alone, is there- 

 fore very great. The colour of the electric light varies 

 according to the materials used as points, between which 

 the arc of flame is produced, as the following experiments 

 will illustrate. 



llsperiment 35. Remove the charcoal points, and in 

 their place insert two of zinc. On bringing these into 

 contact, and again separating them, a most beautiful 

 effect is produced. A vivid blue flame, tinged witli 

 ruby red, is afforded, and the zinc becomes oxidised, 

 producing, in abundance, a flocky-white powder, which 

 has been called " philosophers' wool." 



Experiment 36. Use two points of thick copper wire : 

 a rich green-coloured light is produced, which has a 

 singular optical effect on all surrounding objects, giving 

 thorn a deep-green tint. The face of the experimenter 

 presents a most peculiar appearance, which has often a, 

 most ludicrous effect on an audience, at the lecture- table. 

 Silver affords a rich green colour, of a darker hue than 

 that of copper. 



Experiment 37. Fix two pieces of stout iron wire in 

 the crayon-holders, and bring their points together, 

 taking care that they do not fuse, and so become 

 solidly united. On separating them, a splendid arc of 

 flame will be produced, and the iron will burn with the 

 most brilliant coruscations. Steel affords a still finer 



{ See ante, p. 136. 



