Himalayan Journals Part 55

Temp. of sunk Therm. 68.8 to 68.3 Extreme Temperature of Air observed 75.7 to 58.0 Approximate Mean Temp. of Air deduced 6601 Diff. between Air and sunk Therm. +2.5 ------------------------------------------------------------------- Locality Pomrang Date Sept. 15 to 23 Elevation 5,143 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 70.3 to 68.5 Extreme Temperature of Air observed 73.0 to 57.0 Approximate Mean Temp. of Air deduced 65.5 Diff. between Air and sunk Therm. +3.9 ------------------------------------------------------------------- Locality Pomrang Date Oct. 6 to 10 Elevation 5,143 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 68.3 Extreme Temperature of Air observed 73.7 to 58.2 Approximate Mean Temp. of Air deduced 65.0 Diff. between Air and sunk Therm. +3.3 ------------------------------------------------------------------- * Hole full of rain-water.

SERIES V.--_Jheels, Gangetic Delta, and Chittagong._ ------------------------------------------------------------------- Locality Silchar Date Nov.27 to 30 Elevation 116 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 77.7 to 75.8 Extreme Temperature of Air observed 55.0 to 81.7 Approximate Mean Temp. of Air deduced 69.1 Diff. between Air and sunk Therm. +7.7 ------------------------------------------------------------------- Locality Silhet Date Dec. 3 to 7 Elevation 133 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 73.5 to 73.7 Extreme Temperature of Air observed 63.0 to 74.5 Approximate Mean Temp. of Air deduced 69.5 Diff. between Air and sunk Therm. +3.1 ------------------------------------------------------------------- Locality Noacolly Date Dec. 18 to 19 Elevation 20 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 73.3 Extreme Temperature of Air observed 58.5 to 76.5 Approximate Mean Temp. of Air deduced 69.5 Diff. between Air and sunk Therm. +3.8 ------------------------------------------------------------------- Locality Chittagong Date Dec. 23 to 31 Elevation 191 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 72.5 to 73.0 Extreme Temperature of Air observed 53.2 to 75.0 Approximate Mean Temp. of Air deduced 63.8 Diff. between Air and sunk Therm. +9.0 ------------------------------------------------------------------- Locality Chittagong Date Jan. 14 to 16 Elevation 116 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 73.3 to 73.7 Extreme Temperature of Air observed 61.3 to 78.7 Approximate Mean Temp. of Air deduced 65.5 Diff. between Air and sunk Therm. +8.3 ------------------------------------------------------------------- Locality Chittagong flagstaf hill Date Dec. 28 to 30 Elevation 151 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 72.0 to 71.8 Extreme Temperature of Air observed 55.2 to 74.2 Approximate Mean Temp. of Air deduced 65.3 Diff. between Air and sunk Therm. +6.6 ------------------------------------------------------------------- Locality Hat-hazaree Date Jan.4 to 5 Elevation 20 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 71.3 Extreme Temperature of Air observed 50.5 to 62.0 Approximate Mean Temp. of Air deduced 65.0 Diff. between Air and sunk Therm. +6.3 ------------------------------------------------------------------- Locality Sidhee Date Jan.5 to 6 Elevation 20 feet Depth 2 ft. 7 in.

Temp. of sunk Therm. 71.0 Extreme Temperature of Air observed 52.7 to 70.2 Approximate Mean Temp. of Air deduced 65.0 Diff. between Air and sunk Therm. +6.0 ------------------------------------------------------------------- Locality Hattiah Date Jan.6 to 9 Elevation 20 feet Depth 2 ft. 7 in.

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 at the Mint, etc., by Mr. Muller.

** 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 suns.h.i.+ne. 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 ma.s.ses 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 gra.s.sy 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 pa.s.s through a rarefied atmosphere, and the rocks especially radiating much of the heat thus acc.u.mulated, 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 circ.u.mstances; 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 lat.i.tude 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 t.i.talya 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.

No. of Obs. Temp. Equiv. of 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 ------------------------------------------------------------- 1,324 Mean 344 feet

IL--_Winter or dry season observatians at Dorjiling._

1. Observations taken at Mr. J. Muller's, and chiefly 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.

2. Observations at Dr. Campbell's (Superintendent's) house in April; elev. 6,950 feet; similar exposure to the last. 13 observations in April 1 degree=308 ft.

3. Observations by Mr. Muller at Colinton; elev. 7,179 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.

4. Miscellaneous (11) observations at Leebong; elev. 6000 feet; in February; free exposure all round 1 degree=266 ft.

5. Miscellaneous observations at "Smith's Hotel;"

Dorjiling, on a cleared ridge; exposed all round; elev. 6,863 feet. April and May 1 degree=252 ft.

----------------- Mean of winter observations 1 degree=286 ft.

Mean of summer observations 1 degree=344 ft.

----------------- Mean 310 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._

Number Difference Equivalent Month of Observ. of Temperature 1 degree F.= ------------------------------------------------------------- January 27 30.4 287 ft.

February 84 32.8 265 March 37 41.9 196 April 7 36.0 236 March and April 29 37.3 224 July 83 23.6 389 August 74 22.4 415 September 95 25.7 350 October 18 29.5 297 ------------------------------------------------------------- Sum 454 Mean 31.1 Mean 296 ft.

These, it will be seen, give a result which approximates to that of the sets I and II. Being deduced from observations at different exposures, the effects of these may be supposed to be eliminated.

It is to be observed that the probable results of the addition of November and December's observations, would be balanced by those of May and June, which are hot moist months.

IV.--_Miscellaneous cold weather observations made at various elevations between 1000 and 17,000 feet, during my journey into east Nepal and Sikkim, in November to January 1848 and 1849.

The equivalent to 1 degree Fahr. was deduced from the mean of all the observations at each station, and these being arranged in sets corresponding to their elevations, gave the following results._

Number of Number of Equivalent Elevation Stations Observations 1 degree F.= --------------------------------------------------------------- 1,000 to 4,000 ft. 27 111 215 ft.

4,000 to 8,000 ft. 52 197 315 8,000 to 12,000 ft. 20 84 327 12,000 to 17,000 ft. 14 54 377 --------------------------------------------------------------- Sum 113 Sum 446 Mean 308 ft.

The total number of comparative observations taken during that journey, amounted to 563, and the mean equivalent was 1 degree=303 feet, but I rejected many of the observations that were obviously unworthy of confidence.

V.--_Miscellaneous observations (chiefly during the rainy season) taken during my journey into Sikkim and the frontier of Tibet, between May 2nd and December 25th, 1848. The observations were reduced as in the previous instance. The rains on this occasion were unusually protracted, and cannot be said to have ceased till mid-winter, which partly accounts for the very high temperatures._

Number of Number of Equivalent Elevation Stations Observations 1 degree F.= --------------------------------------------------------------- 1,000 to 4,000 ft. 10 45 422 ft.

4,000 to 8,000 ft. 21 283 336 8,000 to 12,000 ft. 18 343 355 12,000 to 17,000 ft. 29 219 417 --------------------------------------------------------------- Sum 78 Sum 890 Mean 383 ft.

The great elevation of the temperature in the lowest elevations is accounted for by the heating of the valleys wherein these observations were taken, and especially of the rocks on their floors.

The increase with the elevation, of the three succeeding sets, arises from the fact that the loftier regions are far within the mountain region, and are less forest clad and more sunny than the outer Himalaya.

A considerable number of observations were taken during this journey at night, when none are recorded at Calcutta, but which are comparable with contemporaneous observations taken by Mr. Muller at Dorjiling. These being all taken during the three most rainy months, when the temperature varies but very little during the whole twenty-four hours, I expected satisfactory results, but they proved very irregular and anomalous.

The means were--

At 21 stations of greater elevation than Dorjiling 1 degree=348 ft.

At 17 stations lower in elevation 1 degree=447 ft.

VI.--_Sixty-four contemporaneous observations at Jillapahar, 7,430 feet, and the bed of the Great Rungeet river, 818 feet; taken in January and February, give 1 degree=322 feet.

VII.--_Observations taken by burying a thermometer two and a half to three feet deep, in a bra.s.s tube, at Dorjiling and at various elevations near that station._

Month February and March Upper Stations Jillapahar, 7,430 feet Lower Stations Leebong, 6000 feet 1 degree= 269 feet