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Tables of Barometrical and Thermometrical Observations, made in Affgkanistan. Upper Scinde, and Kutch Gundava, during the years 1839-40. By Da. Geiffith.
A copy of these Tables was furnished to the Surveying Officers of the Army of the Indus, as their Barometers ceased to be effective soon after leaving Quettah. No other register was I believe kept.
Columns 8 and 9 require some explanation, they contain the readings off of the Thermometer, Barometer invented by Dr. Woollaston, but with the substitution of an ordinary Thermometer for his delicate one. Of these I have had several in India, but never met with one that was in working order. The great weight and thinness of the bulb, likewise renders them very liable to be broken.
After adjusting the new tubes, and marking on them zero marks corresponding to the zero of the scale, I formed a scale of valuations of each degree from comparisons with the Barometers. I had similar Thermometers in use in Bootan, and have had ample opportunities of knowing that they will intimate altitudes to within trifling differences of travelling Barometers, than which they are much more portable. Ordinary thermometers for ascertaining altitudes by boiling water, vary a good deal, and are not to be depended upon. My instruments are now in Captain Sander's possession, and if they have escaped unbroken, after comparing them with the best barometers in Calcutta, I shall do rcyself the honour of presenting the results to Government.
These Barometrical observations were made with an Englefield's Barometer, and though made in a dry climate, and with every care, as to drying the inside of the tube with a silk sponging-wire, as well as to allow no air-bubbles to remain, can only be considered as approximative. The mercury was not as pure as it might have been, and none of the Chemists in Calcutta could supply me with fresh distilled mercury.
There is also considerable laxity in the columns of attached and detached thermometers owing to breakages, occasional reduction to one mstroment, and the general place of observation, a tent, in different parts of which very various temperatures are to be found.
At I found that screwing, however lightly, the ordinary cistern to the tube (to fix it) occasioned some of the tubes to break, I subsequently, at Cabool, abandoned the plan altogether, and used a wooden box as cistern, ■afBciently large to enable the inverted tube, closed by the forefingers, to be inserted under the liquid; the float was adjusted as usual. I can recommend this plan as a practical one, and much easier than the use of the ordinary cistern.
The instrument was put up afresh every day, even during halts,— 'at tables shew that with care, and using one tube, the readings of varies day8 do not differ very much.