ELEVATION 13,000 TO 14,000 FEET.
EASTERN NEPAL AND SIKKIM.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 7 Mon Lepcha 13,090 Jan. 27.1 18.5 8.6 .122 4 Ditto 13,073 Jan. 25.6 16.4 9.2 .113 2 Tunkra valley 13,111 Aug. 45.0 43.5 1.5 .298 21 Jongri 13,194 Jan. 22.7 10.5 12.2 .091 1 Zemu river 13,281 June 46.7 46.7 0.0 .334 4 Choonjerma 13,288 Dec. 39.0 11.1 27.9 .093 10 Yangma village 13,502 Nov./ 33.8 18.6 15.2 .123 Dec.
1 Wallanchoon road 13,505 Nov. 28.0 9.5 18.5 .088 3 Kambachen, below pa.s.s 13,600 Dec. 40.0 18.6 21.4 .123 --------------------------------------------------------------------- 53 Mean 34.2 21.5 12.6 .154
CALCUTTA.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 7 Mon Lepcha 13,090 Jan. 70.0 50.8 19.2 .527 4 Ditto 13,073 Jan. 71.7 49.9 21.8 .373 2 Tunkra valley 13,111 Aug. 81.2 78.7 2.5 .962 21 Jongri 13,194 Jan. 70.6 53.2 17.4 .417 1 Zemu river 13,281 June 92.9 86.6 6.2 1.230 4 Choonjerma 13,288 Dec. 69.8 61.8 28.0 .555 10 Yangma village 13,502 Nov./ 78.9 62.1 16.8 .561 Dec.
1 Wallanchoon road 13,505 Nov. 66.4 61.8 14.6 .555 3 Kambachen, below pa.s.s 13,600 Dec. 72.9 62.2 10.7 .563 --------------------------------------------------------------------- 53 Mean 74.9 63.0 11.9 .636
Humidity 0.634 Calcutta 0.678 Weight of vapour 1.61 gr. 6.28 gr.
ELEVATION 15,000 TO 16,000 FEET.
EASTERN NEPAL AND SIKKIM.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Yangma valley 15,186 Dec. 42.2 20.7 21.5 .133 1 Choonjerma pa.s.s 15,259 Dec. 34.3 10.5 23.8 .091 8 Lachee-pia 15,262 Aug. 42.0 41.6 0.4 .279 12 Momay, 7 a.m. ,, Sept. 39.4 34.7 4.7 .219 6 ,, 9.50 a.m. ,, Sept. 50.9 41.7 9.2 .280 4 ,, noon ,, Sept. 51.7 43.6 8.1 .299 8 ,, 2.40 p.m. ,, Sept. 49.7 41.9 7.8 .283 10 ,, 4 p.m. ,, Sept. 44.4 41.3 3.1 .276 16 ,, sunset ,, Sept. 41.5 38.6 2.9 .252 8 ,, Miscellaneous ,, Sept. 47.6 41.4 6.2 .277 6 ,, ,, ,, Oct. 40.9 36.5 4.4 .234 3 Sittong 15,372 Oct. 38.6 29.8 8.8 .184 2 Palung 15,676 Oct. 44.6 39.8 4.8 .262 1 Kambachen pa.s.s 15,770 Dec. 26.5 15.9 10.6 .111 1 Yeumtong 15,985 Sept. 44.6 43.7 0.9 .300 --------------------------------------------------------------------- 87 Mean 42.6 34.8 7.8 .232
CALCUTTA.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Yangma valley 15,186 Dec. 80.8 62.0 18.8 .559 1 Choonjerma pa.s.s 15,259 Dec. 77.9 60.6 17.3 .534 8 Lachee-pia 15,262 Aug. 85.5 79.4 6.1 .982 12 Momay, 7 a.m. ,, Sept. 80.5 78.8 1.7 .966 6 ,, 9.50 a.m. ,, Sept. 87.6 78.8 8.8 .963 4 ,, noon ,, Sept. 89.5 79.7 9.8 .990 8 ,, 2.40 p.m. ,, Sept. 90.0 78.3 11.7 .949 10 ,, 4 p.m. ,, Sept. 88.7 77.6 11.1 .928 16 ,, sunset ,, Sept. 84.2 78.4 5.8 .952 8 ,, Miscellaneous ,, Sept. 87.4 78.6 8.8 .956 6 ,, ,, ,, Oct. 83.9 69.3 14.6 .710 3 Sittong 15,372 Oct. 84.0 77.5 6.5 .926 2 Palung 15,676 Oct. 86.8 78.5 8.3 .954 1 Kambachen pa.s.s 15,770 Dec. 78.0 58.5 19.5 .498 1 Yeumtong 15,985 Sept. 88.8 80.5 8.3 1.016 --------------------------------------------------------------------- 87 Mean 84.9 74.4 10.5 .859
Humidity 0.763 Calcutta 0.719 Weight of vapour 2.55 gr. 8.95 gr.
ELEVATION 16,000 TO 17,000 FEET.
EASTERN NEPAL AND SIKKIM.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Kanglachem pa.s.s 16,038 Dec. 32.8 16.3 16.5 .110 3 Tunkra pa.s.s 16,038 Aug. 39.8 38.7 1.1 .252 1 Wallanchoon pa.s.s 16,756 Nov. 18.0-6.0 24.0 .046 5 Teumtso 16,808 Oct. 32.4 25.1 7.3 .156 6 Cholamoo lake 16,900 Oct. 31.4 20.2 11.2 .130 1 Donkia mountain 16,978 Sept. 40.2 25.9 14.3 .160 --------------------------------------------------------------------- 17 Mean 32.4 20.0 12.4 .142
CALCUTTA.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Kanglachem pa.s.s 16,038 Dec. 80.7 61.1 19.6 .543 3 Tunkra pa.s.s 16,038 Aug. 86.0 78.7 7.3 .959 1 Wallanchoon pa.s.s 16,756 Nov. 79.9 57.6 22.3 .483 5 Teumtso 16,808 Oct. 85.0 75.7 9.3 .872 6 Cholamoo lake 16,900 Oct. 79.8 68.4 11.4 .690 1 Donkia mountain 16,978 Sept. 87.6 78.8 18.8 .963 --------------------------------------------------------------------- 17 Mean 83.2 70.1 13.3 .752
Humidity 0.640 Calcutta 0.658 Weight of vapour 1.53 gr. 7.80 gr.
ELEVATION 17,000 TO 18,500 FEET.
EASTERN NEPAL AND SIKKIM.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Kinchinjhow 17,624 Sept. 47.5 30.9 16.6 .191 1 Sebolah pa.s.s 17,585 Sept. 46.5 34.6 11.9 .218 1 Donkin mountain 18,307 Sept. 38.8 35.3 3.5 .224 3 Bhomtso 18,450 Oct. 54.0 4.4 49.6 .072 2 Donkia pa.s.s 18,466 Sept. 41.8 30.3 11.5 .188 2 Ditto 18,466 Oct. 40.1 25.0 15.1 .155 --------------------------------------------------------------------- 10 Mean 44.8 26.8 18.0 .175
CALCUTTA.
No. of Obs. Locality Elev. Month Tem. D.P. Diff. Tens --------------------------------------------------------------------- 1 Kinchinjhow 17,624 Sept. 85.7 79.7 16.0 .991 1 Sebolah pa.s.s 17,585 Sept. 88.8 80.0 18.8 1.002 1 Donkin mountain 18,307 Sept. 90.7 79.3 11.4 .981 3 Bhomtso 18,450 Oct. 91.1 61.1 20.0 .543 2 Donkia pa.s.s 18,466 Sept. 84.1 78.4 15.7 .950 2 Ditto 18,466 Oct. 86.5 65.5 21.0 .627 --------------------------------------------------------------------- 10 Mean 87.8 74.0 12.2 .849
Humidity 0.532 Calcutta 0.648 Weight of vapour 1.90 gr. 8.78 gr.
SUMMARY.
HUMIDITY WEIGHT OF VAPOUR No. of Elevations Sta- Sik-Cal- Diff. Sik-Cal-Diff.
Obs. in Feet tions kim cutta Sikkim kim cutta Sikkim ---------------------------------------------------------------------- 48 735 to 2000 9 .717 .663 +.054 5.57 6.88-1.31 49 2000 to 3000 9 .820 .740 .080 5.45 7.13 1.68 48 3000 to 4000 13 .858 .732 .116 4.23 6.60 2.37 137 4000 to 5000 23 .837 .730 .107 4.33 7.12 2.79 260 5000 to 6000 15 .865 .730 .135 4.70 7.34 2.64 76 6000 to 7000 13 .845 .701 .144 3.60 6.71 3.11 1023 7000 to 8000 14 .826 .668 .158 3.85 7.28 3.43 193 8000 to 9000 13 .858 .730 .128 4.23 8.75 4.52 18 9000 to 10,000 5 .747 .724 .023 2.80 6.28 3.48 123 10,000 to 11,000 10 .878 .740 .138 3.35 8.70 4.35 104 11,000 to 12,000 6 .860 .760 .100 3.46 9.00 5.54 140 12,000 to 13,000 6 .890 .815 .075 3.37 9.75 6.38 53 13,000 to 14,000 9 .634 .678 -.044 1.61 6.28 4.67 87 15,000 to 16,000 8 .763 .719 +.044 2.55 8.95 6.40 17 16,000 to 17,000 6 .640 .658 .018 1.53 7.80 6.27 10 17,000 to 18,500 5 .532 .648 -.116 1.90 8.78 6.88 ---------------------------------------------------------------------- 2386 154
Considering how desultory the observations in Sikkim are, and how much affected by local circ.u.mstances, the above results must be considered highly satisfactory: they prove that the relative humidity of the atmospheric column remains pretty constant throughout all elevations, except when these are in a Tibetan climate; and when above 18,000 feet, elevations which I attained in fine weather only.
Up to 12,000 feet this constant humidity is very marked; the observations made at greater elevations were almost invariably to the north, or leeward of the great snowy peaks, and consequently in a drier climate; and there it will be seen that these proportions are occasionally inverted; and in Tibet itself a degree of relative dryness is encountered, such as is never equalled on the plains of Eastern Bengal or the Gangetic delta. Whether an isolated peak rising near Calcutta, to the elevation of 19,000 feet, would present similar results to the above, is not proven by these observations, but as the relative humidity is the same at all elevations on the outermost ranges of Sikkim, which attain 10,000 feet, and as these rise from the plains like steep islands out of the ocean, it may be presumed that the effects of elevation would be the same in both cases.
The first effect of this humid wind is to clothe Sikkim with forests, that make it moister still; and however difficult it is to separate cause from effect in such cases as those of the reciprocal action of humidity on vegetation, and vegetation on humidity, it is necessary for the observer to consider the one as the effect of the other.
There is no doubt that but for the humidity of the region, the Sikkim Himalaya would not present the uniform clothing of forest that it does; and, on the other hand, that but for this vegetation, the relative humidity would not be so great.* [Balloon ascents and observations on small mountainous islands, therefore, offer the best means of solving such questions: of these, the results of ballooning, under Mr. Welsh"s intrepid and skilful pioneering (see Phil. Trans.
for 1853), have proved most satisfactory; though, from the time for observation being short, and from the interference of belts of vapour, some anomalies have not been eliminated. Islands again are still more exposed to local influences, which may be easily eliminated in a long series of observations. I think that were two islands, as different in their physical characters as St. Helena and Ascension, selected for comparative observations, at various elevations, the laws that regulate the distribution of humidity in the upper regions might be deduced without difficulty. They are advantageous sites, from differing remarkably in their humidity.
Owing partly to the indestructible nature of its component rock (a gla.s.sy basalt), the lower parts of Ascension have never yielded to the corroding effects of the moist sea air which surrounds it; which has decomposed the upper part into a deep bed of clay. Hence Ascension does not support a native tree, or even shrub, two feet high. St. Helena, on the other hand, which can hardly be considered more favourably situated for humidity, was clothed with a redundant vegetation when discovered, and trees and tree-ferns (types of humidity) still spread over its loftiest summits. Here the humidity, vegetation, and mineral and mechanical composition reciprocate their influences.]
The great amount of relative humidity registered at 6000 to 8000 feet, arises from most of the observations having been made on the outer range, where the atmosphere is surcharged. The majority of those at 10,000 to 12,000 feet, which also give a disproportionate amount of humidity, were registered at the Zemu and Thlonok rivers, where the narrowness of the valleys, the proximity of great snowy peaks, and the rank luxuriance of the vegetation, all favour a humid atmosphere.
I would have added the relative rain-fall to the above, but this is so very local a phenomenon, and my observations were so repeatedly deranged by having to camp in forests, and by local obstacles of all kinds, that I have suppressed them; their general results I have given in Appendix F.
I here add a few observations, taken on the plains at the foot of the Sikkim Himalaya during the spring months.
_Comparison between Temperature and Humidity of the Sikkim Terai and Calcutta, in March and April, 1849._
Elev.
No. above TEMP. D.P. TENSION SAT.
of sea.
Obs. Locality Feet C. T. C. T. C. T. C. T.
--------------------------------------------------------------------- 4 Rummai 293 82.2 70.6 61.7 60.5 .553 .532 .517 .717 4 Belakoba 368 92.8 85.5 62.6 63.0 .570 .578 .382 .485 3 Rangamally 275 84.2 75.0 68.7 62.5 .695 .568 .605 .665 3 Bhojepore 404 90.1 81.2 54.1 44.3 .429 .308 .313 .295 4 Thakyagunj 284 84.9 77.1 61.3 60.8 .547 .537 .466 .588 3 Bhatgong 225 87.4 74.9 64.7 54.6 .611 .436 .480 .512 2 Sahigunj 231 80.2 68.0 66.2 53.1 .642 .414 .635 .409 8 t.i.talya 362 85.5 80.0 55.4 56.1 .448 .459 .376 .459 --------------------------------------------------------------------- 31 Means 305 85.9 79.0 61.8 56.9 .562 .479 .472 .516 May, 1850 ) 131 89.7 K78.6 76.7 K71.4 .904 K.759 .665 K.793 Kishengunj) --------------------------------------------------------------------- Vapour in a cubic foot--Kishengunj 8.20 Terai 5.08 Calcutta 9.52 Calcutta 5.90 Mean difference of temperature between Terai and Calcutta, from 31 observations in March, as above, excluding minima Terai--6.9 Mean difference from 26 observations in March, including minima Terai--9.7 Mean difference of temperature at Siligore on May 1, 1850-- 10.9 Mean difference of temperature at Kishengunj on May 1, 1850--11.1
From the above, it appears that during the spring months, and before the rains commence, the belt of sandy and gra.s.sy land along the Himalaya, though only 3.5 degrees north of Calcutta, is at least 6 degrees or 7 degrees colder, and always more humid relatively, though there is absolutely less moisture suspended in the air. After the rains commence; I believe that this is in a great measure inverted, the plains becoming excessively heated, and the temperature being higher than at Calcutta. This indeed follows from the well known fact that the summer heat increases greatly in advancing north-west from the Bay of Bengal to the trans-Sutledge regions; it is admirably expressed in the maps of Dove"s great work "On the Distribution of Heat on the Surface of the Globe."
APPENDIX H.
ON THE TEMPERATURE OF THE SOIL AT VARIOUS ELEVATIONS.
These observations were taken by burying a bra.s.s tube two feet six inches to three feet deep, in exposed soil, and sinking in it, by a string or tied to a slip of wood, a thermometer whose bulb was well padded with wool: this, after a few hours" rest, indicates the temperature of the soil. Such a tube and thermometer I usually caused to be sunk wherever I halted, if even for one night, except during the height of the rains, which are so heavy that they communicate to the earth a temperature considerably above that of the air.
The results proved that the temperature of the soil at Dorjiling varies with that of the month, from 46 degrees to 62.2 degrees, but is hardly affected by the diurnal variation, except in extreme cases.
In summer, throughout the rains, May to October, the temperature is that of the month, which is imparted by the rain to the depth of eleven feet during heavy continued falls (of six to twelve inches a day), on which occasions I have seen the buried thermometer indicating a temperature above the mean of the month. Again, in the winter months, December and January, it stands 5 degrees above the monthly mean; in November and February 4 degrees to 5 degrees; in March a few degrees below the mean temperature of the month, and in October above it; April and May being sunny, it stands above their mean; June to September a little below the mean temperature of each respectively.
The temperature of the soil is affected by:--1. The exposure of the surface; 2. The nature of the soil; 3. Its permeability by rain, and the presence of underground springs; 4. The sun"s declination; 5. The elevation above the sea, and consequently the heating power of the sun"s rays: and 6, The amount of cloud and sunshine.
The appended observations, though taken at sixty-seven places, are far from being sufficient to supply data for the exact estimation of the effects of the sun on the soil at any elevation or locality; they, however, indicate with tolerable certainty the main features of this phenomenon, and these are in entire conformity with more ample series obtained elsewhere. The result, which at first sight appears the most anomalous, is, that the mean temperature of the soil, at two or three feet depth, is almost throughout the year in India above that of the surrounding atmosphere. This has been also ascertained to be the case in England by several observers, and the carefully conducted observations of Mr. Robert Thompson at the Horticultural Society"s Gardens at Chiswick, show that the temperature of the soil at that place is, on the mean of six years, at the depth of one foot, 1 degree above that of the air, and at two feet 1.5 degrees. During the winter months the soil is considerably (l degree to 3 degrees) warmer than the air, and during summer the soil is a fraction of a degree cooler than the air.
In India, the sun"s declination being greater, these effects are much exaggerated, the soil on the plains being in winter sometimes 9 degrees hotter than the air; and at considerable elevations in the Himalaya very much more than that; in summer also, the temperature of the soil seldom falls below that of the air, except where copious rain-falls communicate a low temperature, or where forests interfere with the sun"s rays.
At considerable elevations these effects are so greatly increased, that it is extremely probable that at certain localities the mean temperature of the soil may be even 10 degrees warmer than that of the air; thus, at Jongri, elevation 13,194 feet, the soil in January was 34.5 degrees, or 19.2 degrees above the mean temperature of the month, immediately before the ground became covered with snow for the remainder of the winter; during the three succeeding months, therefore, the temperature of the soil probably does not fall below that of the snow, whilst the mean temperature of the air in January may be estimated at about 20 degrees, February 22 degrees, March 30 degrees, and April 35 degrees. If, again, we a.s.sume the temperature of the soil of Jongri to be that of other Sikkim localities between 10,000 and 14,000 feet, we may a.s.sume the soil to be warmer by 10 degrees in July (see Tungu observations), by 8 degrees or 9 degrees in September (see Yeumtong); by l0 degrees in October (see Tungu); and by 7 degrees to l0 degrees in November (see Wallanchoon and Nanki). These temperatures, however, vary extremely according to exposure and amount of sunshine; and I should expect that the greatest differences would be found in the sunny climate of Tibet, where the sun"s heat is most powerful. Were nocturnal or terrestrial radiation as constant and powerful as solar, the effects of the latter would be neutralised; but such is not the case at any elevation in Sikkim.
This acc.u.mulated heat in the upper strata of soil must have a very powerful effect upon vegetation, preventing the delicate rootlets of shrubs from becoming frozen, and preserving vitality in the more fleshy, roots, such as those of the large rhubarbs and small orchids, whose spongy cellular tissues would no doubt be ruptured by severe frosts. To the burrowing rodents, the hares, marmots, and rats, which abound at 15,000 to 17,000 feet in Tibet, this phenomenon is even more conspicuously important; for were the soil in winter to acquire the mean temperature of the air, it would take very long to heat after the melting of the snow, and indeed the latter phenomenon would be greatly r.e.t.a.r.ded. The rapid development of vegetation after the disappearance of the snow, is no doubt also proximately due to the heat of the soil, quite as much as to the increased strength of the sun"s direct rays in lofty regions.
I have given in the column following that containing the temperature of the sunk thermometer, first the extreme temperatures of the air recorded during the time the instrument was sunk; and in the next following, the mean temperature of the air during the same period, so far as I could ascertain it from my own observations.
SERIES I.--_Soane Valley_ --------------------------------------------------------------------- Locality Muddunpore Date Feb. 11 to 12 Elevation 440 feet Depth 3 ft. 4 in.
Temp. of sunk Therm. 71.5 Extreme Temperature of Air observed 62.0 to 77.5 Approximate Mean Temp. of Air deduced 67.0 Diff. between Air and sunk Therm. +4.5 ----------------------------------------------------- Locality Nourunga Date Feb. 12 to 13 Elevation 340 feet Depth 3 ft. 8 in.