Himalayan Journals, vol 2 by J. D. Hooker (android pdf ebook reader TXT) 📕

Temp. of sunk Therm. 67.7 (shaded by trees)

Extreme Temperature of Air observed 50.2 to 77.5

Approximate Mean Temp. of Air deduced 64.5

Diff. between Air and sunk Therm. +3.2

Locality Seetakoond

Date Jan. 9 to 14

Elevation 20 feet

Depth 2 ft. 7 in.

Temp. of sunk Therm. 73.3 to 73.7

Extreme Temperature of Air observed 55.2 to 79.5

Approximate Mean Temp. of Air deduced 70.2

Diff. between Air and sunk Therm. +3.3

Locality Calcutta*

Date Jan. 16 to Feb. 5

Elevation 18 feet

Depth 2 ft. 7 in.

Temp. of sunk Therm. 76.0 to 77.0

Extreme Temperature of Air observed 56.5 to 82.0**

Approximate Mean Temp. of Air deduced 69.3

Diff. between Air and sunk Therm. +7.2

** Observations for temperature of air, taken at the Observatory.

APPENDIX I.

ON THE DECREMENT OF TEMPERATURE IN ASCENDING THE SIKKIM

HIMALAYA MOUNTAINS AND KHASIA MOUNTAINS.

I have selected as many of my observations for temperature of the sir as appeared to be trustworthy, and which, also, were taken

contemporaneously with others at Calcutta, and I have compared them with the Calcutta observations, in order to find the ratio of

decrement of heat to an increase of elevation. The results of several sets of observations are grouped together, but show so great an

amount of discrepancy, that it is evident that a long series of

months and the selection of several stations are necessary in a

mountain country to arrive at any accurate results. Even at the

stations where the most numerous and the most trustworthy

observations were recorded, the results of different months differ

extremely; and with regard to the other stations, where few

observations were taken, each one is affected differently from

another at the same level with it, by the presence or proximity of

forest, by exposure to the east or west, to ascending or descending currents in the valleys, and to cloud or sunshine. Other and still

more important modifying influences are to be traced to the monthly variations in the amount of humidity in the air and the strength of its currents, to radiation, and to the evolution of heat which

accompanies condensation raising the temperature of elevated regions during the rainy season. The proximity of large masses of snow has

not the influence I should have expected in lowering the temperature of the surrounding atmosphere, partly no doubt because of the more

rapid condensation of vapours which it effects, and partly because of the free circulation of the currents around it. The difference

between the temperatures of adjacent grassy and naked or rocky spots, on the other hand, is very great indeed, the former soon becoming

powerfully heated in lofty regions where the sun's rays pass through a rarefied atmosphere, and the rocks especially radiating much of the heat thus accumulated, for long after sunset. In various parts of my journals I have alluded to other disturbing causes, which being all more or leas familiar to meteorologists, I need not recapitulate

here. Their combined effects raise all the summer temperatures above what they should theoretically be.

In taking Calcutta as a standard of comparison, I have been guided by two circumstances; first, the necessity of selecting a spot where

observations were regularly and accurately made; and secondly, the

being able to satisfy myself by a comparison of my instruments that the results should be so far strictly comparable.

I have allowed 1 degree Fahr. for every degree in latitude

intervening between Sikkim and Calcutta, as the probable ratio of

diminution of temperature. So far as my observations made in east

Bengal and in various parts of the Gangetic delta afford a means of solving this question, this is a near approximation to the truth. The spring observations however which I have made at the foot of the

Sikkim Himalaya would indicate a much more rapid decrement; the mean temperature of Titalya and other parts of the plains south of the

forests, between March and May being certainly 6 degrees-9 degrees

lower than Calcutta: this period however is marked by north-west and north-east winds, and by a strong haze which prevents the sun's rays from impinging on the soil with any effect. During the southerly

winds, the same region is probably hotter than Calcutta, there being but scanty vegetation, and the rain-fall being moderate.

In the following observations solitary readings are always rejected.

I.--Summer or Rainy Season observations at Dorjiling.

Observations taken during the rainy season of 1848, at Mr. Hodgson's (Jillapahar, Dorjiling) alt. 7,430 feet, exposure free to the north east and west, the slopes all round covered with heavy timber; much mist hence hangs over the station. The mean temperatures of the month at Jillapahar are deduced from horary observations, and those of

Calcutta from the mean of the daily maximum and minimum.

Month at Jillapahar Temp. Calcutta 1 degree F.

July 284 61.7 86.6 364 feet

August 378 61.7 85.7 346 feet

September 407 58.9 84.7 348 feet

October 255 55.3 83.3 316 feet

IL--Winter or dry season obaervatians at Dorjiling.

by himself, at "the Dale;" elev. 6,956 feet; a

sheltered spot, with no forest near, and a free

west exposure. 103 observations. Months: November,

December, January, and February 1 degree=313 ft.

house in April; elev. 6,950 feet; similar exposure

to the last. 13 observations in April 1 degree=308 ft.

feet; free exposure to north-west; much forest about

the station, and a high ridge to east and south.

38 observations in winter months 1 degree=290 ft.

elev. 6000 feet; in February; free exposure all

round 1 degree=266 ft.

Dorjiling, on a cleared ridge; exposed all round;

elev. 6,863 feet. April and May 1 degree=252 ft.

III.--_Miscellaneous observations taken at different places in

Dorjiling, elevations 6,900 to 7,400 feet, with the differences of

temperature between Calcutta and Dorjiling._

Month of Observ. of Temperature 1 degree F.=

January 27 30.4 287 ft.

February 84 32.8