358 



NATURE 



{August 10, 1S82 



cally sealed glass ball, perfectly exhausted, the filament stiffers no 

 apparent change even when heated to an extreme degree of while- 

 ness. This result was reached in 1S78. It has since then become 

 clearly evident that Mr. Edison had the same idea and reached 

 the same conclusion as Mr. Steam and myself. 



A necessary condition of the higher vacuum was the simplifica- 

 tion of the lamp. In its construction there must be as little as 

 possible of any material, and there must be none of such material 

 as could occlude gas, which being eventually given out would 

 spoil the vacuum. There must besides be no joints except those 

 made by the glass-blower. 



Therefore, naturally and per force of circumstances, the incan- 

 descent carbon lamp took the most elementary form, resolving 

 itself into a simple bulb, pierced by two platinum wires supporting 

 a filament of carbon. Probably the first lamp, having this ele- 

 mentary character, ever publicly exhibited, was shown in opera- 

 tion at a meeting of the Literary and Philosophical Society of 

 Newcastle in February, 1879. The vacuum had been produced 

 by Mr. Steam by means of an improved Sprengel pump of his 

 invention. 



Blackening of the lamp glass, and speedy breaking of the 

 carbons, had been such invariable accompaniments of the old 

 conditions of imperfect vacua, and of imperfect contact between 

 carbon and conducting wires, as to have led to the conclusion 

 that the carbon was volatilised. But under the new conditions 

 these faults entirely disappeared ; and carefully conducted expe- 

 riments have shown that well-made lamps are quite serviceable 

 after more than a thousand hours' continual use. 



Here are some specimens of the latest and most perfected 

 forms of lamp. The mode of attaching the filament to the 

 conducting wires by means of a tiny tube of platinum, and 

 also the improved form of the lamp, are due to the skill of Mr. 

 Gimmingham. 



The lamp is easily attached and detached from the socket 

 which connects it with the conducting wires ; and can be adapted 

 to a great variety of fittings, and these may he provided with 

 switches or taps for lighting or extinguishing the lamps. I have 

 here a lamp fitted especially for use in mines. The current may 

 be supplied either through main wires from a dynamo-electrical 

 machine, with flexible branch wires to the lamp, or it may be fed 

 by a set of portable store cells closely connected with it. I will 

 give you an illustration of the quality of the light these incan- 

 descent lamps are capable of producing by turning the current 

 from a Siemens' dynamo-electric machine (which is working by 

 means of a gas engine in the basement of the building) through 

 sixty lamps ranged round the front of the gallery and through 

 six on the table. (The theatre was now completely illuminated 

 by means of the lamps, the gas being turned off during the rest 

 of the lecture.) 



It is evident by the appearance of the flowers on the table that 

 colours are seen very truly by this light, and this is suggestive of 

 its suitability for the lighting of pictures. 



The heat produced is comparatively very small ; and of course 

 there are no noxious vapours. 



And now I may, I think, fairly say that the difficulties 

 encountered in the construction of incandescent electric lamps 

 have been completely conquered, and that their use is economi- 

 cally practicable. In making this statement I mean, that, both 

 as regards the cost of the lamp itself and the cost of supplying 

 electricity to illuminate it, light can be produced at a cost which 

 will compare not unfavourably with the cost of gas light. It is 

 evident that if this opinion can be sustained, lighting by elec- 

 tricity at once assumes a position of the widest public interest, 

 and of the greatest economic importance ; and in view of this, I 

 may be permitted to enter with some detail into a consideration 

 of the facts which support it. 



There has now been sufficient experience in the manufacture of 

 lamps to leave no doubt that they can be cheaply constructed, 

 and we know by actual experiment that continuous heating to a 

 fairly high degree of incandescence during 1200 hours does not 

 destroy a well-made lamp. What the utmost limit of a lamp's 

 life may be we really do not know. Probably it will be an ever- 

 increasing span; as, with increasing experience, processes of 

 manufacture are sure to become more and more perfect. Taking 

 it, therefore, as fully established that a cheap and durable lamp 

 can now be made, the further question is as to thecost of the means 

 of its illumination. 



This question in its simplest form is that of the more or less 

 economical use of coal ; for coal is the principal raw material 

 alike in the production of gas and of electric light. In the one 



case, the coal is consumed in producing gas which is burnt ; in 

 the other in producing motive power, and, by its means, 

 electricity. 



The cost of producing light by means of electric incandescence 

 may be compared with the cost of producing gas-light in this 

 way — 2 cwt. of coal produces icoo cubic feet of gas, and this 

 quantity of gas, of the quality called fifteen-candle gas, will pro- 

 duce 3000 candle-light for one hour. But besides the product 

 of gas, the coal yields certain bye-products of almost equal 

 value. I will, therefore, take it that we have in effect 1000 feet 

 of gas from I cwt. of coal instead of from 2, as is actually the 

 case. 



And now, as regards the production of electricity. One cwt. 

 of coal— that is the same measure in point of value as gives 1000 

 feet of gas — will give 50 horse-power for one hour. Repeated 

 and reliable experiments show that we can obtain through the 

 medium of incandescent lamps at least 200 candle-light per 

 hor-e-power per hour. But as there is waste in the conversion 

 of motive power into electricity, and also in the conducting- 

 wires, let us make a liberal deduction of 25 per cent., and take 

 only 150 candle-light as the nett available | roduct of I horse- 

 power ; then for 50 horse-power (the product of I cwt. of coal), 

 we have 7500 candle-light, as against 30CO candle-light from an 

 equivalent value of gas. That is to say, two and a half times 

 more light. 



There still remains an allowance to be made to cover the cost 

 of the renewal of lamps. There is a parallel expense in connec- 

 tion with gas lighting in the cost of the renewal of gas-burners, 

 gas globes, gas chimnies, &c. I cannot say that I think these 

 charges against gas-lighting will equal the corresponding charges 

 against electric lighting, unless we import into the account — as I 

 think it right to do — the consideration that, without a good deal 

 of expense be incurred in the renewal of burners, and unless 

 minute attention be given, far beyond what is actually given, to 

 all the conditions under which the gas is burned, nothing like 

 the full light product which I have allowed to be obtainable 

 from the burning of loco cubic feet of gas, will be obtained, 

 and, as a matter of fact, is not commonly obtained, especially in 

 domestic lighting. Taking this into account, and considering 

 what would have to be done to obtain the full yield of light from 

 gas, and that if it be not done, then the estimate I have made is 

 too favourable, I think but little, if any, greater allowance need 

 be made for the charge in connection with the renewal of lamps 

 in electric lighting than ought to be made for the corresponding 

 charges for the renewal of gas-burners, globes, chimneys, &c. 

 But it will be seen that even if the cost for renewal of lamps 

 should prove to be considerably greater than the corresponding 

 expense in the case of gas, there is a wide margin to meet them 

 before we have reached the limit of the cost of gas-lighting. 



I think too it must be fairly taken into account and placed to 

 the credit of electric lighting, that by this mode of lighting there 

 is entire avoidance of the damage to furnishings and decora- 

 tions of houses, to books, pictures, and to goods in shops, 

 which is caused through lighting by gas, and which entails a 

 large expenditure for repair, and a large amount of loss which 

 is irreparable. 



1 have based these computations of cost of electric light on 

 the supposition that the light product of 1 horse-power is 150 

 candles. But if durability of the lamps had not to be considered, 

 and it were an abstract question how much light can be obtained 

 through the medium of an incandescent filament of carbon, then 

 one might, without deviating from ascertained fact, have spoken 

 of a very much larger amount of light as obtainable by this 

 expenditure of motive power. I might have assumed double or 

 even more than double the light for this expenditure. Certainly 

 double and treble the result I have supposed can actually be 

 obtained. The figures I have taken are those which consist 

 with long life to the lamps. If we take more light for a given 

 expenditure of power, we shall have to renew the lamps oftener, 

 and so what we gain in one way we lose in another. But it is 

 extremely probable that a higher degree of incandescence than 

 that on which I have based my calculations of cost, may prove 

 to be compatible with durability of the lamps. In that case, 

 the economy of electric lighting will be greater than I have 

 stated. 



In comparing the cost of producing light by gas and by elec- 

 tricity, I have only dealt with the radical item of coal in both 

 cases. Gas-lighting is entirely dependent upon coal — electric 

 lighting is not, but in all probability coal will be the chief source 

 of energy in the electric lighting also. When, however, water 



