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ELECTRICAL IMAGES. 



ELECTRICAL LIGHT. 



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alcohol, sulphide of carbon, &c.,' be introduced. In no case does the 

 light appear to be continuous, but to consist of a succession o: 

 discharges, more or less rapid, according to the rate of oscillation 

 of the hammer of the coil. The luminous zones appear to have a 

 double movement of gyration and undulation, which have been 

 regarded by some as an optical illusion, since by causing the hammer 

 to oscillate slowly, the zones appear to be distinct and fixed. The 

 effects can also be produced with a continuous current from a very 

 strong battery, but an intermitting current requires only a single 

 pair, and in this case, any increase in the power of the battery does 

 not appear to increase the effects. M. Gaugain has endeavoured to 

 show that the variations in the light belong to various strata o) 

 vapours contained within the glass, and that the electricity assists the 

 arrangement of these vapours into strata. 



ELECTRICAL IMAGES. Under the article BREATH-FIGUBES, will 

 be found a number of curious details respecting the production oi 

 electro-graphic images or figures. Lichtenberg's figures are produced 

 by tracing on a cake of resin any marks or figures with the knob of a 

 Leyden jar, charged first positively and then negatively, and project- 

 ing on the cake a coloured compound non-conducting powder, such as 

 sulphur and red-lead, triturated together. The powder will render 

 the characters visible ; because, in rubbing them up, they become 

 electrified by the friction, the sulphur + and the red-lead , so that 

 when the powder is blown over the resin, the sulphur is attracted by 

 those parts which are negatively electrified, and the red-lead to those 

 which are positively electrified. 



A curious class of electrical images connected with the theory of 

 the distribution of electricity, has been investigated by Professor 

 William Thomson, of Glasgow. The effect of an electrified body on 

 an uninsulated sphere is represented by the image of the electrified 

 body in the sphere. So also, when an electrified body is placed near 

 two uninsulated spheres, an inductive effect is produced, represented 

 by an infinite series of successive images in each sphere. If again a 

 conductor bounded by segments of two spherical surfaces cutting at 

 an angle which is a sub-multiple of two right angles, be electrified by 

 induction, the effect may be represented by a finite number of images 

 placed symmetrically in the circumference of a circle passing through 

 the exciting or inducing body, and cutting the two spherical surfaces 

 at right angles, similarly to the symmetrically arranged images of a 

 kaleidoscope. Mr. Murphy, in his treatise on ' Heat and Electricity,' 

 had previously adopted what he called " the principle of successive 

 influences," for the purpose of obtaining numerical approximations to 

 the state of electrified bodies influencing each other, by calculating 

 the effects of four or five successive acts of influences. 

 ELECTRICAL LAMP. [ELECTRIC LIGHT.] 

 ELECTRICAL, or ELECTRIC LIGHT. The most splendid 

 artificial light known is that produced by the current of a powerful 

 voltaic battery between two pencils of hard charcoal, such as that 

 deposited in the retorts of gas works. The charcoal, which is an 

 imperfect conductor, becomes incandescent, and as it is not fusible at 

 any known temperature, the splendour of the light is only limited by 

 the power of the battery. The charcoal is formed into pointed cylinders, 

 three or four inches in length, mounted in metallic holders connected 

 with the ends of the voltaic battery, and the pencils are fixed, so that 

 their points may be easily brought into contact or made to recede 

 from each other as required. When in contact, the current passes 

 between them, and the charcoal becomes eminently luminous. When 

 separated, a splendid flame passes between them, and this flame is not 

 symmetrical with respect to the two poles, for that portion of it next 

 the positive point has the greatest diameter, and as it approaches the 

 negative point, the diameter gradually diminishes. This light can be 

 produced in an exhausted receiver, under water, or in gases which do 

 not support combustion. 



This light has been applied by M. Foucault with great effect as a 

 substitute for the lime light in the gas microscope. The apparatus as 

 constructed by M. Dubosc, and called by him a photo-electric micro- 

 Kope, contains a self -ad justing apparatus, the object of which is to 

 preserve a nearly uniform brilliancy in the light, notwithstanding the 

 gradual waste of the charcoal. Hitherto the difficulty has been to 

 regulate the h'ght so as to keep the two points at nearly the same 

 distance from each other. The regulators of Messrs. Staite and Petrie 

 in this country, and those of several inventors in France, were in- 

 tended to produce this result. It will perhaps be sufficient if we here 

 describe the photo-electric apparatus of M. Delcuil. It consists of a 

 tripod of cast iron on which are fixed the two charcoal pencils and 

 the regulator which maintains a constant interval between them. 

 The negative pencil, N, is held by a metal support, the wire of which 

 slides through a hole in the knob, D, with slight friction, so that this 

 pencil once adjusted remains fixed. The positive pencil, p, on the con- 

 trary, ia so arranged that in proportion as the distance between the 

 pencils tends to increase, the action of the voltaic current causes it to 

 rise. The regulator by which this result is attained is attached to the 

 lower part of the tripod, but is represented on a larger scale in a 

 separate figure, for both of which we are indebted to the 7th edition 

 of M. Ganot's ' Traite elementaire de Physique,' 1857. A is a lever 

 attached at one end to a spiral spring B, so that it can oscillate upon 

 the pivot L through a very small space, the other end being fixed 

 between the point* of a vice, capable of being adjusted at pleasure. 



AB.T8 USD SCL DIV. VOL. III. 



Now this lever tends to turn in one direction by the action of the 

 spring, B, and in a contrary direction by the action of an electro- 



magnet, E. At the end of the lever near B is a steel spring, the upper 

 end of which, at I, is engaged in the teeth of a ratched bar, K, on the 

 top of which is a holder of the positive pencil P. Now it is evident 

 that when the current circulates with full force through the wire of 

 the electro-magnet, the latter strongly attacks the iron armature, m, 

 attached to the lever, A, whereby the arm of the lever to the right of 

 L descends through a small space, and causes the steel spring, I, to slip 

 into one of the lower teeth of the ratchet bar. This motion does not 

 cause the ratchet bar to descend, since the upper part of the steel 

 spring is curved in such a way as to exert no resistance in descending, 

 but only in ascending. If, however, the distance between the pencils 

 p and N increase, the electrical current becomes weaker, the electro- 

 magnet loses somewhat of its attractive force, and not being able to 

 counteract the action of the spiral spring, B, the latter draws up its 

 end of the lever, and with it the steel spring, I, the effect of which is 

 to raise the bar, K, a quarter of a mLfiemetre. No sooner are the 

 charcoal points brought nearer together, than the current resumes its 

 former intensity, and the electro-magnet acts as before, the steel 

 spring slips into a lower tooth ready to raise the bar when the current 

 becomes enfeebled by the increased distance caused by the wasting 

 away of the charcoal points. The screw at c is for regulating the 

 spiral spring, B. In both figures the direction of the current is 

 indicated by arrows. The charcoal points are preserved from the 

 cooling action of the air by being enclosed in a tube of glass, and a 

 metallic reflector allows the light to be directed and concentrated at 

 any required spot. 



Now that the electric light has been brought under control, it is of 

 course a question of expense, as in the case of electro-motive apparatus, 

 whether we shall employ our coal in smelting the metals which are to 

 be burnt in the voltaic battery, for procuring a source of illumination, 

 or whether our coal may not be more economically employed in gene- 

 rating street gas. This light has been employed in France to give 

 light to the workmen employed at night in excavating the docks at 

 Cherbourg ; two sets of apparatus were used, each maintained with one 

 of Bunsen's large batteries of 50 pairs, and these were sufficient to give 

 light to 800 workmen, at the total cost of 14 francs 55 c. for each 

 apparatus. The light has also been employed by night in certain 

 public works in Great Britain. 



MM. Fizeau and Foucault have endeavoured to compare the electric 

 light with that of the sun, by means of the chemical effects produced 

 by each source on plates of iodide of silver. Taking the intensity of 

 the solar light at midday at 1000, the electric light from 46 pairs of 

 Bunsen, was represented by 235, while with 80 pairs it was only 238. 

 The intensity of the light, in fact, does not increase with the number 

 of pairs, but with the extent of surface. With three series of 46 pairs 

 each, arranged so that all the positive poles should meet in one, and 

 the negative poles also in one, the effect of which was to triple the 

 amount of surface, the intensity was 385, or more than one-third that 

 of solar light. Bunsen found that 48 pairs not arranged for producing 

 ;he greatest effect, yielded a light equal to the united effect of 672 wax 

 caudles. 



The electric light determines the combination of a mixture of chlo- 

 rine and hydrogen, and acts on chloride of silver in the same manner 

 as solar light. When passed through a prism, a spectrum is produced 



81 



