252 _ Scientific Intelligence. : [Marcny 
2. Another formula, very easy of computation, is the following ; 
(59 — 3) x 10(B—2) x (1 + 0023 T) 
This. is accurate when the mean height of the mercury is either 
29 or 30 inches; and very nearly so for any elevation not exceeding 
700 or 800 yards above the sea. Where the mean height is much 
Jess than 283 inches, the error becomes progressively important. 
The easiest way of correcting the logarithmic result for difference 
of atmospheric temperature is by means of the third factor in my 
second formula; in which T expresses the difference between the 
mean temperature and 31°. The first formula includes this correc- 
tion; and on that account may be compared in point of facility, as 
well as correctness, with any method of computation yet known. 
Iam yours, most respectfully, 
Bath, Feb. 13, 1817. W. G. Horner. 
P.S. Does not the excessive dryness of the atmosphere so 
eloquently described by Col. Beaufoy sufficiently explain the unex- 
pected result of his experiment with the burning lens on the 
summit of Mont Blanc? 
XVI. Improvement suggested in the new Blow-pipe of Mr. Brooke. 
(To Dr, Thomson.) 
DEAR SIR, Feb. 6, 1817. 
Being a constant reader of your Annals of Philosophy, and ob- 
serving several proposals for improving the gaseous blow-pipe, but 
thinking none of them perfectly safe, I venture the following ideas. 
Suppose there was a circular hole in the bottom made as large as 
the reservoir would permit, with a thin piece of tin or lead soldered 
over it, this secured over a hole in a table, under which is placed a 
tub of sand. If an explosion should take place, the piece soldered 
on will be driven into the tub. This, in addition to Professor 
Cumming’s contrivance, and the oil of Professor Clarke, would, I 
conceive, ensure perfect safety. 
N.B. I have constructed a gaseous blow-pipe on the preceding 
principle. It is a circular vessel of cast-iron, with a flat top and 
bottom, eight inches in diameter, and four inches deep inside mea- 
sure, and half an inch thick. At the bottom there is a circular hole 
five inches in diameter. Over this hole is placed a piece of thin 
lead, secured with an iron flange or ring, oiled leather, and screws. 
The reservoir stands upon four feet. ‘Thus complete, it is placed 
over a hole in the table, &c. as before mentioned. Fitting up the 
apparatus myself, and requiring a valve to open into the reservoir, I 
made one, I think, on an improved principle. It is of brass, in 
the form of a cone, accurately ground into the lower extremity of 
the condenser, and secured with a piece of India rubber stretched 
through an eye on the base of the cone, and fastened with waxed 
