90 On the aériform Compounds 
In calculating the corrections of A and S three places of the 
logarithms are sufficient. 
D—d=1"5 
Log. 1"5, ‘0°176 Log. 15 0176 
Sin 8, 9-899 Cos S, 9-785 
A.C. sin ¢, 10-417 Tana, 10-059 
Log 3'l, ~ 0492 A.C. sin ¢, 10°417 
‘ Log 2:7 0437 
A = 48° 533 S.== 52. 28) 
— 31 27 
48 50"2 52 30"7 
true latitude. true hor. angle of M. T. 
The method that has been explained requires only the easy 
lemma for computing the ares ZD and DO, and the rules for 
solving right-angled spherical triangles; and it is an advantage 
that every step is the calculation of some part of the figure, bv 
which circumstance the memory is assisted. The process here 
followed is also preferable to the other methods in leading to 
the determination of the problem, or in pointing ont which of 
the two possible solutions is the true one, when this ean be done. 
In the extensive Nautical Tables published by the late Mr. Men- 
doza, there is one for assisting the direct solution of this pro- 
blem. It contains the base, and likewise the angle at the base, 
of the isosceles triangle A P B formed by the two circles of decli- 
nation. A similar table that should contain the perpendicular 
PO of the same triangle, and likewise half the base AO, or 
rather the sine and co-sine of AO, would render the preceding 
method by far the shortest of any hitherto proposed. But the 
use of such tables is not free from objection, and ought not to be 
adopted unless a great advantage is gained. 
August 6, 1521. J. Ivory. 
XVII, On the aériform Compounds of Charcoal and Hydrogen; 
with an Account of some additional Experiments on the Gases 
from Oil and from Coal. By Wm. Henry, M.D. F.R.S. 
: [From the Transactions of the Royal Society. ] 
Tue experiments on the aériform compounds of charcoal and 
hydrogen, described in the following pages, are supplementary 
to a Memoir on the same class of bodies, which the Royal Society 
did me the honour to insert in their Transactions for 1808*, as 
well as to other papers on the same subject, which have been 
published in Mr. Nicholson’s Journal, and in the Memoirs of the 
Manchester Society. Of these essays, I beg leave to offer avery 
* See Phil. Mag. vol. xxxii. p. 277. 
. brief 
