Himalayan Journals, vol 2 by J. D. Hooker (great reads TXT) 📖
- Author: J. D. Hooker
- Performer: -
Book online «Himalayan Journals, vol 2 by J. D. Hooker (great reads TXT) 📖». Author J. D. Hooker
Number of Observations 35
1 degree= 345 feet
Altitude above the Sea 5,302 feet
Moflong
Date June, July, Aug., Oct.
Calcutta Observations 85.9 degrees
Number of Observations 73
Khasia Observations 68.8 degrees
Number of Observations 74
1 degree= 373 feet
Altitude above the Sea 6,062 feet
Syong
Date
Calcutta Observations 85.1 degrees
Number of Observations 4
Khasia Observations 65.0 degrees
Number of Observations 6
1 degree= 332 feet
Altitude above the Sea 5,734 feet
Myrung
Date August
Calcutta Observations 89.1 degrees
Number of Observations 42
Khasia Observations 69.7 degrees
Number of Observations 41
1 degree= 343 feet
Altitude above the Sea 5,632 feet
Myrung
Date October
Calcutta Observations 82.9 degrees
Number of Observations 21
Khasia Observations 63.2 degrees
Number of Observations 58
1 degree= 336 feet
Altitude above the Sea 5,632 feet
Nunklow
Calcutta Observations 86.4 degrees
Number of Observations 139
Khasia Observations 70.9 degrees
Number of Observations 139
1 degree= 372 feet
Altitude above the Sea 4,688 feet
Mooshye
Date September 23
Calcutta Observations 78.5 degrees
Number of Observations 9
Khasia Observations 66.3 degrees
Number of Observations 12
1 degree= 499 feet
Altitude above the Sea 4,863 feet
Pomrang
Date September 23
Calcutta Observations 82.7 degrees
Number of Observations 51
Khasia Observations 65.8 degrees
Number of Observations 51
1 degree= 369 feet
Altitude above the Sea 5,143 feet
Amwee
Date September 23
Calcutta Observations 79.9 degrees
Number of Observations 15
Khasia Observations 67.1 degrees
Number of Observations 11
1 degree= 396 feet
Altitude above the Sea 4,105 feet
Joowy
Date September 23
Calcutta Observations 79.5 degrees
Number of Observations 11
Khasia Observations 69.0 degrees
Number of Observations 7
1 degree= 567 feet
Altitude above the Sea 4,387 feet
Total Calcutta Observations 400
Total Khasia Observations 434
Mean 1 degree= 385 feet
The equivalent thus deduced is far greater than that brought out by the Sikkim observations. It indicates a considerably higher
temperature of the atmosphere, and is probably attributable to the
evolution of heat during extraordinary rain-fall, and to the
formation of the surface, which is a very undulating table-land, and everywhere traversed by broad deep valleys, with very steep, often
precipitous flanks; these get heated by the powerful sun, and from
them, powerful currents ascend. The scanty covering of herbage too
over a great amount of the surface, and the consequent radiation of heat from the earth, must have a sensible influence on the mean
temperature of the summer months.
APPENDIX J.
ON THE MEASUREMENT OF ALTITUDES BY THE BOILING-POINT THERMOMETER.
The use of the boiling-point thermometer for the determination of
elevations in mountainous countries appearing to me to be much
underrated, I have collected the observations which I was enabled to take, and compared their results with barometrical ones.
I had always three boiling-point thermometers in use, and for several months five; the instruments were constructed by Newman, Dollond,
Troughton, and Simms, and Jones, and though all in one sense good
instruments, differed much from one another, and from the truth.
Mr. Welsh has had the kindness to compare the three best instruments with the standards at the Kew Observatory at various temperatures
between 180 degrees and the boiling-point; from which comparison it appears, that an error of l.5 degrees may be found at some parts of the scale of instruments most confidently vouched for by admirable
makers. Dollond's thermometer, which Dr. Thomson had used throughout his extensive west Tibetan journeys, deviated but little from the
truth at all ordinary temperatures. All were so far good, that the
errors, which were almost entirely attributable to carelessness in
the adjustments, were constant, or increased at a constant ratio
throughout all parts of the scale; so that the results of the
different instruments have, after correction, proved strictly
comparable.
The kettle used was a copper one, supplied by Newman, with free
escape for the steam; it answered perfectly for all but very high
elevations indeed, where, from the water boiling at very low
temperatures, the metal of the kettle, and consequently of the
thermometer, often got heated above the temperature of the
boiling water.
I found that no confidence could be placed in observations taken at great elevations, by plunging the thermometer in open vessels of
boiling water, however large or deep, the abstraction of heat from
the surface being so rapid, that the water, though boiling below, and hence bubbling above, is not uniformly of the same temperature
throughout.
In the Himalaya I invariably used distilled, or snow or rain-water; but often as I have tried common river-water for comparison, I never found that it made any difference in the temperature of the
boiling-point. Even the mineral-spring water at Yeumtong, and the
detritus-charged glacial streams, gave no difference, and I am hence satisfied that no objection can be urged against river waters of
ordinary purity.
On several occasions I found anomalous rises and falls in the column of mercury, for which I could not account, except theoretically, by assuming breaks in the column, which I failed to detect on lifting
the instrument out of the water; at other times, I observed that the column remained for several minutes stationary, below the true
temperature of the boiling water, and then suddenly rose to it.
These are no doubt instrumental defects, which I only mention as
being sources of error against which the observer must be on the
watch: they can only be guarded against by the use of two
instruments.
With regard to the formula employed for deducing the altitude from a boiling-point observation, the same corrections are to a great extent necessary as with barometric observations: if no account is taken of the probable state of atmospheric pressure at the level of the sea at or near the place of observation, for the hour of the day and month of the year, or for the latitude, it is obvious that errors of 600 to 1000 feet may be accumulated. I have elsewhere stated that the
pressure at Calcutta varies nearly one inch (1000 feet), between July and January; that the daily tide amounts to one-tenth of an inch
(=100 feet); that the multiplier for temperature is too great in the hot season and too small in the cold; and I have experimentally
proved that more accuracy is to be obtained in measuring heights in Sikkim, by assuming the observed Calcutta pressure and temperature to accord with that of the level of the sea in the latitude of Sikkim, than by employing a theoretical pressure and temperature for the
lower station.
In the following observations, the tables I used were those printed by Lieutenant-Colonel Boileau for the East India Company's Magnetic Observatory at Simla, which are based upon Regnault's Table of the
'Elastic Force of Vapour.' The mean height of the barometrical column is assumed (from Bessel's formula) to be 29.924 at temp. 32 degrees, in lat. 45 degrees, which, differing only .002 from the barometric
height corresponding to 212 degrees Fahrenheit, as determined
experimentally by Regnault, gives 29.921 as the pressure
corresponding to 212 degrees at the level of the sea.
The approximate height in feet corresponding to each degree of the
boiling-point, is derived from Oltmann's tables. The multipliers for the mean temperature of the strata of atmosphere passed through, are computed for every degree Fahrenheit, by the formula for expansion
usually employed, and given in Baily's Astronomical Tables and Biot's Astronomie Physique.
For practical purposes it may be assumed that the traveller, in
countries where boiling-point observations are most desired, has
never the advantage of a contemporaneous boiling-point observation at a lower station. The approximate difference in height is hence, in
most cases, deduced from the assumption, that the boiling-point
temperature at the level of the sea, at the place of observation, is 212 degrees, and that the corresponding temperature of the air at the level of
Comments (0)