92 REPORT—1843. 
Substituting then in this expression, instead of v, the value of the length of the column 
" 
f jp and for 

of air between the stations supposed dry, and at 32°, viz. m x log P 
p, t, and f", their proper mean values as already explained, the barometric formula 
finally becomes 
a p=f" 461 +3 (t + 4) V(p—I9 xX WFO 
Dm X18 p= BX 498 7 PNY x GEIS PY 
I may add here, that the correction for moisture is far from being insignificant in 
its amount, as may be seen by the following example. Let us suppose that, when the 
approximate height corrected for temperature amounts to 2700 feet (a height reached 
by several of our Irish mountains), the mean value of the pressure to be used in the 
final factor of the formula is 27-3, and of the force of vapour °3 of an inch, then 
the elongation of the aérial column resulting from moisture is +35 = goth of 2700= 
80 feet. It will, of course, have been observed, that the correction for aqueous va- 
pour differs from that for temperature in the circumstance of being always positive ; 
and this coincides perfectly with the observation I have had frequent occasion of 
making, viz. that heights calculated by the formula in general use, are all appre- 
eisiily leit than the truth. I may, in conclusion, observe, that in assuming—with 
the view of calculating the expansion produced by moisture—that the pressure to be 
employed is the geometric mean of the corrected pressures got by observation at the 
two stations, I am quite aware that I am assigning to it but an approximate value. 
An exact expression for the pressure to be employed admits of being investigated ; but 
its introduction into the formula, while it would give this latter complexity of form, 
and thus render it less suited for practical use, would conduct to results not appre- 
ciably different from those given by the more simple method just explained. 

Observations with the Thermometer made at Aden in Arabia. 
By Corporal Witx1am Moyes. 
The following summary of these observations was drawn up by the Marquis of 
Northampton :— 
Greatest height in the shade occurred at 12 and 2 on the Ist and 2nd, 100°. 
Greatest height in the sun on the Ist, 120°, 
Least in the shade at 2 a.m., 4th, 82°. 
Least in the sun at 8 in the evening, 13th, 14th, 15th, 94°, 
Greatest rise in an hour in the sun at 10 in the morning, 15th, from 94° to 109°. 
Greatest morning variation in the sun, 6th and 7th, from 96° to 108°; and on the 
27th and 28th, from 108° to 98°, 
Greatest evening variation in the sun on the 7th and 8th, from 108° to 100°; and 
on the 26th and 27th, from 104° to 96°, 
Greatest morning variation in the shade, 11th and 12th, from 85° to 88°; and on 
the 13th and 14th, from 86° to 89°. 
Greatest variation in the shade at noon on the 6th and 7th, 98° to 90°. 
Greatest variation in the shade in the evening, 24th and. 25th, 89° to 85°; 26th and 
27th, 85° to 89°; 28th and 29th, 90° to 86°. 
Greatest variation at noon in the sun, 6th and 7th, 106° to 121°, 
On the quantity of Rain which falls in the south-west of Ireland, and in 
Suffolk, with the wind at the several points of the Compass. By the Rev. 
Tuomas Knox and the Rev. Henry Knox. Communicated by Professor 
Lioyp. 
The instrument employed in these observations was contrived by the Rev. Thomas 
Knox, for the purpose of registering the amount of rain which falls at a given place, 
with the wind in different points of the compass. - A description of its construction has 
