'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎77] (98/458)

WEIGHT OF DRY AIR.
Ixxvii
The results given in the last column show.what amount of vapour must exist in the atmos
phere to produce the tension at the lowest points and this is so much greater than what is pos
sible under the known conditions of the rapid decrease in the temperature in ascending the
surface that I fe el quite satisfied that the theory cannot be maintained. The science of Mete-
ordogy has frequently suffered from too ready reception of first principles, and the attention of
its promoters has been turned from questions of real importance to the science to others of only
local value. For example, this reception of the theory of the hygrometer, and belief that it gave
the total quantity of vapour, has discouraged any attempts to approximate, to the truth by other
means. Up to the present time I do not know of any series of observations on evaporation that
are of the slightest value. It is obvious that those made in shallow vessels either in the sun or
shade, exposed to a current of air or protected from it, do not represent anything that takes place
over any considerable portion of the earth’s surface. I would therefore recommend to the
Society to endeavour to obtain, from different stations on the coast, the Mauritius, and other
places, observations of the amount of evaporation from the surface of the sea, tanks, and
earth. The evaporation from the surface of the earth 'might be obtained by an instrument
such as was suggested by Dr. Buist some time since, but inserted into the earth so as to be in
exactly the same circumstances as the surrounding soil. The evaporation from the surface of
the sea which is the most important element of the total evaporation, would be easily found
by the evaporation from the surface of a vessel sunk into the sea so as to have the water within
in exactly the same physical conditions as the sea itself.
To prevent any misconception of my meaning, I must repeat, that while I deny that the
correction of the barometer for pressure of vapour is to be made by subtracting the tension of
vapour at the surface. I do not believe, as some have done, that the presence of vapour
diminishes the only thing that we can with confidence assert on the subject is, that the baro
meter shows the weight of the whole vertical column ; what may be the weight of the several
parts, depends on their vertical distribution. This principle carefully examined, will lead to
some interesting results, to which I hope soon to be able to direct the attention of the Society.
A discussion ensued in reference to several points connected with this paper, and Command
er Jenkins volunteered to commence a preliminary series of observations in Bombay Harbour
in the manner suggested.
The maps, charts, and globes, of the Ross Testimonial, having just been opened, were exhibit
ed before the meeting, and the committee which had been appointed at the last meeting
to superintendent the disposition of them, commenced operations.
The following letters, papers, and books, received since the last meeting, were laid on the
table, and their donors desired to be thanked for the same.
Letters.
1. From Dr Morehead, Principal, Grant Medical College, No, 50 of 1851, dated 15th
August, transmitting for the Library of the Society, a copy of the Report of the Grant Medical
College for the Session 1850-51.
2. From Brigadier Reid, Ahmednuggur, dated 27th August 1851, acknowledging the receipt
of the Society’s letter of the 20th instant, and informing that Captain Gaisford, Instructor of
the Artillery Depot, or Surgeon Mackenzie, of the Artillery, will be most happy to take charge
of the self-registering wind and rain-gauge the S ociety contemplate employing at that station.
From Commander Montriou, Superintendent of the Observatory,'dated 25th August, forward-
by direction of the Right Hon’ble the Governor in Council, for presentation to the Bombay