162 ARTIFICIAL ILLUMINATION. 
vapour, and the illuminating power, as you see, is very much increased. 
Only a small burner, such as No. 1, may be used; otherwise, as the gas 
is so rich in carbon, the flame may smoke badly unless a special air 
supply be provided. Albo-carbon burners, properly managed, are 
very efficient, as much as 6 candle power being obtainable from each 
cubic foot of, thus enriched, London gas burnt per hour, which repre- 
sents an efficiency nearly 100 per cent. higher than that given even by 
the London Argand. Of course there is the cost of the naphthaline 
to be taken into account, but that is comparatively small. But if the 
burner be too large for the air supply the flame will readily smoke, with 
the usual unpleasant effects in the room and the necessity for a more 
frequent white-washing of the ceiling. 
And now we come to “ Regenerative” gas lighting, for the prin- 
ciple of which we are primarily indebted to the late Sir William 
Siemens who introduced the system of utilising waste heat in his re- 
generative furnaces. These furnaces, as you know, have by their. 
economy of coal saved millions of money to this and other countries. 
In them, as you are aware, the hot gases are made to pass through 
intricate flues, to which they impart their heat which would otherwise 
be thrown away. When a flue is sufficiently hot the products of com- 
bustion are diverted into another similar flue and the air supply for the 
furnaces drawn through the one which had just been heated, thus con- 
veying again to the fire the heat which would ordinarily have escaped, 
with the result that a much more intense combustion is produced. The 
principle of a regenerative lamp is precisely the same. The heated 
products of combustion pass through passages in the body of the lamp 
_ above the flame which, as in the small regenerative lamp burning now 
before you, is exceedingly hot, and the air supply to the flame is drawn 
through other passages through the same heated material. Thus, 
instead of the flame being fed by the cool air of the room, it is supplied 
with air which is already at a very high temperature, the result being 
that the incandescence of the carbon in the flame is far more intense 
than if the temperature were kept down, as it usually is, by a cold air 
supply. In this way the intrinsic illumination of ordinary London 
gas can be doubled or trebled. Frankland was probably the first to 
introduce the regenerative principle into gas lighting. He applied it 
with some success to an Argand burner by means of a double chimney. 
For the modern developments of the system we are indebted to the 
successive labours of Grimston, Bower, Thorpe, Wenham and Thomas, 
and also to a very great extent to Siemens. A brilliant example of 
the Siemens regenerative lamp is now burning in the centre of this 
hall, and may be credited, I think, with an illuminating efficiency, 
vertically beneath it, of at least 10 or 12 candle power per cubic foot 
of gas. ‘The average all-round efficiency of a moderate-sized regener- 
ative lamp may be taken at about 6 candle power per cubic foot. This, 
compared with ordinary open burners, you will admit, represents a 
very marked advance in the economy of gas lighting. 
Probably the regenerative lamps of the “ Wenham” company have 
had the greatest commercial success, but that company, like many 
others, has been practically ruined by the latest development of gas 
lighting, the “ Welsbach” or incandescent system, to which I will 
