1817.) Scientific Intelligence. 487 
or horn to allow sufficient emission of light. All the parts must be 
so constructed as to allow no passage for the air but through the 
alter-mentioned openings. The bottom is so fitted as to allow of 
being taken off for the introduction of the oil lamp, A. Two cir- 
cular rims, B, C, are made to fit the inner and outer sides of the 
case. The piece, D, is bent into an obtuse angle (say 110°), both 
sides of which are cut into very fine parallel passages extending all 
round for supplying the lamp with air. In the lower edge of the 
outer case passages are cut; but, instead of being continued all 
round, are divided into eight or ten equal passages, with the same 
number and size of intervening spaces uncut. Thus the circum- 
ference is divided into 16 or 20 sets of spaces alternately open and 
shut. ‘The outer rim of the bottom is also similarly divided and 
cut ; so that by turning the bottom round to the extent of one of the 
spaces, you either completely shut or completely open the passages. 
The three conical tops (E, 1, 2, 3,) are cut into fine parallel vertical 
slits. The air passages may be from -3, to 54, of an inch in length, 
and must not exceed =. or =, part of an inch in width: indeed, the 
finer the openings, the greater security is afforded. They should 
be cut with a sharp chisel upon a leaden block, and the sharp edge 
or bore should be made to stand outwards, in opposition to the cur- 
rent of air rushing inwards. The air must pass through three of 
these gratings before it can reach the flame. 
The small drawing (Fig. 11) represents the lantern proposed in my 
last letter to be fixed on the jets. Itis simply an Argand’s glass 
chimney covered with tin plate, and so cut as to allow free diffusion 
of light all around. The top and bottom are each composed of one 
horizontal and one upright air grating. 
I learn from Mr. Wilson, a young medical gentleman belonging 
to the navy, that canvas pipes are there actually applied to purposes 
similar to what I suggested in my last letter. 
Canvas tubes intended for ventilation may be constructed in the 
following manner :—Provide a wooden mould of the form, length, 
and size, of the intended tubes; also rings of wire for each end, 
and a slip as long as the tubes of plate or hoop iron, into which two 
or more staples or hooks must be riveted for suspending each tube 
by itself. The canvas is then to be cut into pieces, so long and so 
wide that about three inches shall overlap the mould. Then each 
piece is to be coated with strong paint, and applied round the mould. 
The iron slip is now to be inserted into the double part, where it is 
secured by a sowing on each side. The rings are also to be secured 
by sowing ; and, lastly, the whole may be covered over with an 
outside coating of paint. 
It must be obvious to you that in the engraving, Plate LXV. 
Fig. 5, the two arrows intended to represent the current of air from 
the unshaded lateral tubes into the main tube are wrongly directed, 
Iremain, Sir, with great respect, 
Your most obedient servant, 
Glasgoy, April 24, 1817. Huan WaALLacy, 
