'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎4] (23/458)

PE0CEEDING8 OE THE SOCIETY-
a good air pump with barometer gauge £but it seems surprising that any difficulty should be
experienced in determining a matter so simple and so important as this, when a few strokes
of the pump would settle it satisfactorily, without the necessity of ascending an elevation
at all. Mr Dent quotes Professor ^Lloyd's authority on the subject of an air pump
experiment—his views were most favorable to the aneroid, and altogether opposed to
those of Mr Adie. Mr Glassher, of the Greenwich Observatory, again, holds very lightly
of the value of the instrument. I took our own Aneroid to the top of Bapdieu Ghaut
along with me—the following were the results; but, as already stated, the instrument was
unserviceable, so that no conclusion from its indications can in this case bo drawn—the
perfection of the Mountain Sympiesometer is very remarkable
Bapdieu Ghaut, August 23.
Barometer I. Sympiesometer.
Poona, 7 a. ..-.27-952 28‘050
Bapdieu Ghaut, 9 a. ,.. 9 * .....26‘747 26*850
Thermometer.
76
74
1-205 1-200
The barometer is corrected for temperature to 32°.
ft The Barometer at the Colaba Observatory stood on the 23rd August at 29*845, or 1.893
higher than that at Poona: if to this bo added .030 for the difference between 7 a. m., at
which the upper instrument, and 10 a. m, at which the lower one, was read, we shall have
a difference of 1-923, or, adding 3 for ^difference of elevation betwixt the Colaba and
Sewree standard, almost exactly the same as that originally set down as the result of the
first comparison. At Poona the range between the 26th and 31st July was about .040,
that at Bombay about -070—that for the latter part of August at Bombay about • 090 I
have no note of the Poona range of tins date, but assume it at 6 , and have taken the half.
While in Poona I took with me three Aneroids with a sympiesometer into the carriage^
and drove over the station to see with what facility the instruments could be employed in
flying surveys. I did this repeatedly. On one occasion I was accompanied by Colonel Grant,
on another by Captain Studdert; it is needless to give details—compared with the barome
ter the coincidences were of course always wonderful : on one occasion we took a series of
levelled stations, where the accuracy was surprising. The great recommendation, both in
their case and that of the sympiesometer, was the facility with which they could be observ-
ed: by pulling up the horses for a couple of minutes the scale could be read and marked at
once, and one hundredth of an inch being allowed for ten feet of change of level, which
it is at this elevation pretty nearly, no reductions of any sort were requisite—these could
be performed at home afterwards. It is quite clear that the makers of the instrument at
home have generally underrated its value for survey purposes. It is in its present form in
many cases unworthy of the high state of instrument making. The scale, for example,
ought always to extend round the whole dial plate so as to read as low as twenty-three in
ches, and to be cut out at the very extremity of the diameter of the plate ,—by this means
it would be enlarged by nearly a third. Each division corresponding to an inch in the ba
rometer would thus become 18- inches in length, and each tenth of an inch might be divided
into tent hs, instead of quarters as at present. Troughton often cuts the scale of his ma~
rine barometers into hundredths of an inch, so as to be read without a vernier—each of the
divisions recommended would be four*fifths on those referred to ; still a vernier might very