£6 Drs Christison and Turner on the Construction of 
Having now examined the chief circumstances that affect the light given 
out by coal and oil gas during their combustion, we shall conclude this part of 
the subject by a short summary of what has been ascertained, with the view 
of settling the precise construction of the burners. 
When the diameter of the jet-holes is small, the flame is streaked with 
blue ; when great, with yellow. The diameter which answers t best for coal- 
gas, supposing its specific gravity to vary from 550 to 650, is a 32d of an 
inch; and for oil-gas, varying in specific gravity between 900 and 1000, a 
50th of an inch. 
If the distance of the jet-holes from each other is too great, the jet flames 
do not meet, and the light is streaked with blue ; and the nearer they are to 
each other, till they meet completely, the more is the flame bright and uni- 
form. . 
When the central air-aperture is small, the tendency of the flame is to 
burn brown and imperfectly ; when the aperture is great, the tendency of the 
flame is, on the contrary, to burn bright, and with too great vivacity. 
When the jet-holes are large, and near each other, and the central air- 
aperture is small, the glass chimney must be narrow, and vice versa. 
Finally, the most brilliant, and at the same time the most economical light, 
is procured when the jet-holes are very numerous, the air-aperture small, and 
the chimney narrow. 
If, in choosing a burner, therefore, it was requisite to consult only beauty 
and economy, we should unquestionably recommend that they be constructed 
on the principle of the 25-holed burner, described in the last page. But un- 
fortunately the glass is so very near the flame, that the slightest agitation of 
the air, or motion of the glass, or increase in the flow of the gas, causes it to 
smoke, and strike the chimney. For the latter reason, in particular, it can 
never be used by the customers of a public company ; because it would be ne- 
cessary for every one to reduce the flame of his burners whenever a few lights 
were extinguished in his neighbourhood. In order to remedy this inconve- 
nience, the burners of a public company must always be so constructed as to 
burn the gas at some loss ; and on that account, we have recommended that 
the number of holes on a circle of ^ths in diameter, should not exceed 15. 
The glass chimneys for the four sizes of burners formerly mentioned (p. 23.), 
should be T s oths, |§ths, j§ths, and fgths; and their length should be about 
6 inches. As the mouth of the first of these would be too much obstructed by 
the cross-bars of the glass-holder, it should be enlarged a little at the bottom, 
like those for Argand oil-lamps, the contraction being just at the beginning of 
the flame. 
III. 
The last subject we have to consider, is the relative Illuminating power of 
Oil and Coal Gas. 
For ascertaining this point, various methods have been proposed, more 
simple than actual measurement of the light. These methods have been all 
deduced more or less directly from the elaborate papers of i)r Henry of Man- 
chester, on the composition of the Illuminating Gases. He found that they 
all contain a dense gas, the olefiant, which burns with a clear white flame, and 
