ARTIFICIAL ILLUMINATION. 163 
now ask your attention. We have seen that in the ordinary system 
the carbon in the gas, by the incandescence of which light is ob- 
tained, being combustible, has constantly to be renewed. It would 
be an obvious economy if, instead of deriving our light from incan- 
descent carbon, which is destroyed immediately after it has come to be 
useful, we could insert in the flame some refractory substance which 
could be made to glow by the heat of the burning gases and not be con- 
sumed. Ifwe were to do this we should be only utilising the heat-giving 
value of the gas, and might do almost as well without the expensive 
heavy hydro-carbons. The lighter and cheaper constituents of the gas 
have high heat-giving values, and we could utilise the poor gas to raise 
to incandescence, by ‘the heat of its combustion, this refractory sub- 
stance which, once introduced, might remain there practically for ever. 
Some 14 years. ago efforts were made to realise this by the introduction 
of a mantle of fine platinum gauze into a Bunsen flame, none of the 
light-giving value of the gas being used, but only the thermal value 
being utilised to render this mantle incandescent. This was the principle 
of the “ Lewis ” incandescent light, which had for some time a certain 
amount of practical success. It had two disadvantages however : 
(1) It required a high pressure air supply which had to be obtained 
by mechanical means; and (2) it was found that aftor continued use 
the mantle deteriorated in consequence of the formation of carbide of 
platinum. The best installation I ever saw of this light was at the 
Gower Street railway station, where the requisite pressure was obtained 
by an auxiliary engine, but after running for about a year ib was 
removed. For household purposes, of course, the necessity for a pressure 
four or five times as great as that supplied in the mains made the Lewis 
system practically useless. I have myself used a burner of this kind 
with some success, with the help of a specially induced draught, but it 
was more interesting as an experiment than of practical utility. Simi- 
lar difficulties were experienced with the “Clamond” light, which was 
practically the “ Lewis” light with a mantle of fine magnesia threads 
in the place of the platinum gauze, and no more success attended the 
introduction of this system than the Lewis light experienced. 
Shortly after the practical failure of the Lewis and the Clamond 
systems had been proved, Auer von Welsbach produced a mantle which 
has now at length, after eight or nine years’ steady improvement, met 
with a grand success. Although an enormous price, I believe some- 
thing like £200,000, was paid by the English company for their patent 
in this invention, yet, on account of the extreme delicacy and want of 
permanence in radiating power of the mantles first made, the system 
met at the outset with so little success that the company was at one 
time upon the verge of bankruptcy. At this critical time, however, an 
improved mode of manufacture and a better formula for the com- 
position of the material of the mantle were evolved, and a marked 
improvement rapidly brought the new light into favour with the 
result that the incandescent system is now a great commercial 
success and is admitted to be far the most economical and brilliant 
method of gas lighting. . 
Let me tell you in a few words how the mantle is made. . A small 
cotton sack, or little stocking, I may call it, is first knitted, and then 
