'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎103] (124/458)

PRESENTS. cii{
'rhe motion of Mr. Smith, for the purchase of the Blue Books for 1848 and 1851, published by
the Admiralty was put and agreed to.
Professor Patton read extracts of a letter, from Colonel Sykes to Dr* Buist, in reference to his
paper on the correction of the barometer for tension of vapour, and entered into a lengthened
explanation of some points which had been misunderstood. In the paper, he stated he had
been chiefly anxious to show the incorrectness of the present mode of making this correction ;
but had not substituted any thing in its place, because he conceived that in the present state of
our knowledge it Was impossible to separate the effects of the two components of the
atmospheric pressure—the dry air and vapour. The barometer, he said, shows the total
weight of a vertical column of the atmosphere, and it is impossible, without a knowledge of the
mode in which vapour is distributed in the atmosphere, to determine its weight from its tension
at the surface. The origin of this mistake is to be traced to Dalton’s theory of gases of differ
ent kinds having no mutual action. Consequently, Vapour, which is considered as a gas, is
unaffected by the dry air, and can only retain its tension at the surface, by the pressure of its
own particles. But this theory having been proved untrue it will follow, as a necessary con
sequence, that the tension of vapour at the surface gives no indication of the total amount of
vapour in the air, and cannot, therefore, be subtracted from the height of the barometer to give
the pressure of the dry air. It cannot be denied, however, that whatever vapour exists in the
air does actually press on the barometer with its whole weight. To believe otherwise would
be to suppose that vapour had a principle of lightness in itself, and was not acted on by gravity.
This affords a complete refutation of the idea broached by Colonel Sykes in his paper on the
Meteorology of India, published in the last volume of Philosophical Transactions. He maintains
that vapour, mingling with the dry air, expands it and makes it lighter, and in this way he
accounts for the fall of the barometer before rain by the greater quantity of vapour then present
in the air. According to him some correction should be added to the height of the barometer,
in order to obtain the pressure of dry air.
In both these theories there is an element of truth which gives them plausibility ; but both are
in opposition to certain physical laws, and must be abandoned.
The observations of the Wet and Dry bulb Thermometers, and of Daniell’s Hygrometer
ought not to be neglected, since they give nearly correct indications of one of the most import
ant climatic agents,—the state of moisture at the place of observation. These opinions have
been submitted with great humility, and only after long deliberation and experiment; but they
deserve consideration although opposed to the views of Daniell, Sabine, Divy, Glaisher
Dove, Sykes, and almost all the principal meteorologists of the present day, who have written
on the subject. Truth, in scientific matters, cannot be decided by authority, and is only to be
arrived at by a free discussion on every point liable to dispute. The question now treated of
must be admitted to be in that doubtful state, and it is believed that good will result from
a reconsideration of it, although the views here put forward should not be ultimately confirmed.
Letters were read from Lieut. Fergusson, and Messrs. Smith, Elder & Co.
Presents to theLibrary.
Bombay Magnetical and Meteorological Observations for 1848. Presented by Government.
Journal of the Indian Archipelago and Eastern Asia, for the month of October.
Meteorological Abstract kept at the Surveyor General’s office, Calcutta, for January, 1852,
The Meeting then adjourned,