"معاملات الجمعية الجغرافية في بومباي، من يناير ١٨٤٧ حتى مايو ١٨٤٩. تحرير السكرتير. المجلد VIII." [‎٨‎١] (٤٩٦/٩٧)

Ixxxi
ordered out in 1843, and been purchased by Government in January 184G ; of a pair
of self-registering Thermometers, by Newman, and a large Tide-Gauge by Bunfc f
The wind and rain-gauge and tide-gauge last named were of large size, and beauti
ful construction. No drawings or account of them had accompanied them;
they were completely dissected when received, not a screw or pin having been left
in its place. They appeared to have been used, and on being put up again were
found to be beautiful instruments, apparently in good order, with the exception of
two of the springs of the wind pressure plate being absent. They were supposed
to be the instruments supplied some ten years since to the Madras Government, to
whom, from the packing boxes, they appeared to have been addressed, for use on
the Malabar Coast> and that they had been received by the Bombay Government,
in Feb. 1845, since which time they seemed to have been at the presidency unemployed.
It was suggested that as rain hardly ever fell along the coasts of Cutch or Scinde,
and as the Phoonda Ghaut observations were not likely to extend beyond a single
year, the wind and rain-gauge should be sent to Major Jacob, Sawunt Warree.
The tide-gauge was by Bunt, of Bristol : a full account of it was given in the
Philosophical Transactions for 1838. It was so large and so delicate, so trouble
some to remove, and was likely to incur so much expense in its fitting up, that it
was considered advisable to detain it at the Presidency, where it might be employ
ed as a standard, a cheaper instrument, which would suit as well for outstations,
and not cost so much fitting up in all as would the fitting up of Bunt’s instrument
alone, to be sent in its place. The matter was referred to the Committee on Phy
sical Research.
The Secretary made some remarks on the methods usually resorted to for deter
mining heat and evaporation—stating that, though apparently simple, they were
two of the most delicate and troublesome operations the meteorologist had to deal
with. After giving a multitude of illustrations of this, he noticed a curious phe
nomenon that had made its appearance while he was engaged in investigating
evaporation from the soil compared with that from a surface of pure water. The ob
jects and details of the experiment were as follow :—As the evaporation from a
shallow dish of water exposed to the sun, and liable to be raised to a temperature
of 100 or 120°, gives no idea whatever of the amount of evaporation from the sur
face of the sea, large poois, or lakes, which vary but little in temperature, he was
c.nxious to determine the amount of evaporation from the surface of wet earth, com
pared with that from the surface of a considerable mass of water. With this view
two zinc cylinders were produced, three feet in length, and four inches in diameter,
and secured by a strong brass ring at the top and bottom, carefully turned. These
contained fifteen pounds, or a gallon and a half of water each, temperature 82°,
or nineteen pounds of the loose redearth to be found associated with trap rock.
M hen filled with earth well shaken down, they were able to take in six and a half
pounds of water before overflowing. Each was provided with a glass tube quar
ter-inch bore, connected with the bottom of the cylinder, and running parallel with
it as its axis to the top: this was intended to show how high the water stood inside.
The tubes were provided with scales divided into inches and tenths from top to
bottom. On filling one of the cylinders with earth, and then adding water till it
flowed over, that in the tube of course first rose to the level of that hi