Himalayan Journals, vol 2 - J. D. Hooker (bill gates best books txt) 📗

67.4 degrees

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