AND ON PREVENTING ITS EXPLOSION. 53 
extinguishing the flame. But even this is easily obviated, by. 
admitting the air at any height from the floor which may be. 
found requisite. 
“Mats D. page 42.—To. the observations in the text, on the 
construction of the lamp, a few details may be added. 
The principal circumstance requiring adjustment, is that of 
the size of the apetture by. which-the heated air escapes. If it 
is not sufficiently wide, the flame is faint, and'on the move- 
ment of the lamp becomes unsteady, and is liable to be extin- 
guished. If it be too wide, there may be some risk of a cur- 
rent of air entering the lantern by it, especially if the under 
tube is not sufficiently wide, by which the whole security from 
the method would be lost. The due size is most easily found, by 
affixing to the aperture»at the top a conical tube, and cutting 
this down in-successive trials, until. the diameter is, attained at 
which the flame is steady and bright., It is-not easy to give. a 
precise dimension, as the flame is dependent.on the breadth 
and height of the wick, the purity of the oil, and the state of | 
the air; but I find that in a lantern of the. size of the move- 
able one mentioned in the text,—five inches in height by 
three in width, with a flat cotton-wick three-tenths of an inch 
broad, and burning so. as. to consume about two ounces of oil 
in six hours, the diameter of the aperture being a.very.little 
less than half an inch, admitted of the flame being steady and ' 
bright when the combustion was fully established. In the 
mine it may be required to be a little larger. When the lamp 
is kindled, it remains for a minute or two more faint, and if 
moved hastily i in this state, is liable to be extinguished.. One 
aperture is preferable to two or three smaller apertures, as there 
is less risk of any counter-current ; and to guard also against 
this in. any movement of the lamp, it is proper to have the — 
opening 
