Chapter XXXVIII: Appendix: A (3)

Nocturnal and solar radiation, the one causing the formation of dew and hoar-frost when the air in the shade is above freezing, end killing plants by the rapid abstraction of heat from all their surfaces which are exposed to the clear sky, and the other scorching the skin and tender plants during the day, are now familiar phenomena, and particularly engaged my attention during my whole Indian journey. Two phenomena particularly obstruct radiation in Sikkim—the clouds and fog from the end of May till October, and the haze from February till May. Two months alone are usually clear; one before and one after the rains, when the air, though still humid, is transparent. The haze has never been fully explained, though a well-known phenomenon. On the plains of India, at the foot of the hills, it begins generally in the forenoon of the cold season, with the rise of the west wind; and, in February especially, obscures the sun’s disc by noon; frequently it lasts throughout the twenty-four hours, and is usually accompanied by great dryness of the atmosphere. It gradually diminishes in ascending, and have never experienced it at 10,000 feet; at 7000, however, it very often, in April, obscures the snowy ranges 30 miles off, which are bright and defined at sunrise, and either pale away, or become of a lurid yellow-red, according to the density of this haze, till they disappear at 10 a.m. I believe it always accompanies a south-west wind (which is a deflected current of the north-west) and dry atmosphere in Sikkim.

The observations for solar radiation were taken with a black-bulb thermometer, and also with actinometers, but the value of the data afforded by the latter not being fixed or comparative, I shall give the results in a separate section. (See Appendix K.) From a multitude of desultory observations, I conclude that at 7,400 feet, 125·7°, or +67° above the temperature of the air, is the average maximum effect of the sun’s rays on a black-bulb thermometer[413] throughout the year, amounting rarely to +70° and +80° in the summer months, but more frequently in the winter or spring. These results, though greatly above what are obtained at Calcutta, are not much, if at all, above what may be observed on the plains of India. This effect is much increased with the elevation. At 10,000 feet in December, at 9 a.m., I saw the mercury mount to 132° with a difl: of +94°, whilst the temperature of shaded snow hard by was 22°; at 13,100 feet, in January, at 9 a.m., it has stood at 98°, diff. +68·2°; and at 10 a.m., at 114°, diff. +81·4°, whilst the radiating thermometer on the snow had fallen at sunrise to 0·7°. In December, at 13,500 feet, I have seen it 110°, diff. +84°; at 11 a.m., 11,500 feet; 122°, diff: +82°. This is but a small selection from many instances of the extraordinary power of solar radiation in the coldest months, at great elevations.

[413] From the mean of very many observations, I find that 10° is the average difference at the level of the sea, in India, between two similar thermometers, with spherical bulbs (half-inch diam.), the one of black, and the other of plain glass, and both being equally exposed to the sun’s rays.

Nocturnal and terrestrial radiation are even more difficult phenomena for the traveller to estimate than solar radiation, the danger of exposing instruments at night being always great in wild countries. I most frequently used a thermometer graduated on the glass, and placed in the focus of a parabolic reflector, and a similar one laid upon white cotton,[414] and found no material difference in the mean of many observations of each, though often 1° to 2° in individual ones. Avoiding radiation from surrounding objects is very difficult, especially in wooded countries. I have also tried the radiating power of grass and the earth; the temperature of the latter is generally less, and that of the former greater, than the thermometer exposed on cotton or in the reflector, but much depends on the surface of the herbage and soil.

[414] Snow radiates the most powerfully of any substance I have tried; in one instance, at 13,000 feet, in January, the thermometer on snow fell to 0·2°, which was 10·8° below the temperature at the time, the grass showing 6·7°; and on another occasion to 1·2°, when the air at the time (before sunrise) was 21·2°; the difference therefore being 20°. I have frequently made this observation, and always with a similar result; it may account for the great injury plants sustain from a thin covering of ice on their foliage, even when the temperature is but little below the freezing-point.

The power of terrestrial, like that of solar radiation, increases with the elevation, but not in an equal proportion. At 7,400 feet, the mean of all my observations shows a temperature of 35·4°. During the rains, 3° to 4° is the mean maximum, but the nights being almost invariably cloudy, it is scarcely on one night out of six that there is any radiation. From October to December the amount is greater=10° to 12, and from January till May greater still, being as much as 15°. During the winter months the effect of radiation is often felt throughout the clear days, dew forming abundantly at 4000 to 8000 feet in the shaded bottoms of narrow valleys, into which the sun does not penetrate till 10 a.m., and from which it disappears at 3 p.m. I have seen the thermometer in the reflector fall 12° at 10 a.m. in a shaded valley. This often produces an anomalous effect, causing the temperature in the shade to fall after sunrise; for the mists which condense in the bottom of the valleys after midnight disperse after sunrise, but long before reached by the sun, and powerful radiation ensues, lowering the surrounding temperature: a fall of 1° to 2° after sunrise of air in the shade is hence common in valleys in November and December.[415] The excessive radiation of the winter months often gives rise to a curious phenomenon; it causes the formation of copious dew on the blanket of the traveller’s bed, which radiates heat to the tent roof, and this inside either an open or a closed tent. I have experienced this at various elevations, from 6000 to 16,000 feet. Whether the minimum temperature be as high as 50°, or but little above zero, the effect is the same, except that hoar-frost or ice forms in the latter case. Another remarkable effect of nocturnal radiation is the curl of the alpine rhododendron leaves in November, which is probably due to the freezing and consequent expansion of the water in the upper strata of cells exposed to the sky. The first curl is generally repaired by the ensuing day’s sun, but after two or three nights the leaves become permanently curled, and remain so till they fall in the following spring.

[415] Such is the explanation which I have offered of this phenomenon in the Hort. Soc. Journal. On thinking over the matter since, I have speculated upon the probability of this fall of temperature being due to the absorption of heat that must become latent on the dispersion of the dense masses of white fog that choke the valleys at sunrise.

I have said that the nocturnal radiation in the English spring months is the great obstacle to the cultivation of many Himalayan plants; but it is not therefore to be inferred that there is no similar amount of radiation in the Himalaya; for, on the contrary, in April its amount is much greater than in England, frequently equalling 13° of difference; and I have seen 16° at 7,500 feet; but the minimum temperature at the time is 51°, and the absolute amount of cold therefore immaterial. The mean minimum of London is 38°, and, when lowered 5·5° by radiation, the consequent cold is very considerable. Mr. Daniell, in his admirable essay on the climate of London, mentions 17° as the maximum effect of nocturnal radiation ever observed by him. I have registered 16° in April at Dorjiling; nearly as much at 6000 feet in February; twice 13°, and once 14·2° in September at 15,500 feet; and 10° in October at 16,800 feet; nearly 13° in January at 7000 feet; 14·5° in February at that elevation, and, on several occasions, 14·7° at 10,000 feet in November.

The annual rain-fall at Dorjiling averages 120 inches (or 10 feet), but varies from 100 to 130 in different years; this is fully three times the amount of the average English fall,[416] and yet not one-fourth of what is experienced on the Khasia hills in Eastern Bengal, where fifty feet of rain falls. The greater proportion descends between June and September, as much as thirty inches sometimes falling in one month. From November to February inclusive, the months are comparatively dry; March and October are characterised by violent storms at the equinoxes, with thunder, destructive lightning, and hail.

[416] The general ideas on the subject of the English rain-fall are so very vague, that I may be pardoned for reminding my readers that in 1852, the year of extraordinary rain, the amounts varied from 28·5 inches in Essex, to 50 inches at Cirencester, and 67·5 (average of five years) at Plympton St. Mary’s, and 102·5 at Holme, on the Dart.

The rain-gauge takes no account of the enormous deposition from mists and fogs: these keep the atmosphere in a state of moisture, the amount of which I have estimated at 0·88 as the saturation-point at Dorjiling, 0·83 being that of London. In July, the dampest month, the saturation-point is 0·97; and in December, owing to the dryness of the air on the neighbouring plains of India, whence dry blasts pass over Sikkim, the mean saturation-point of the month sometimes falls as low as 0·69.

The dew-point is on the average of the year 49·3°, or 3° below the mean temperature of the air. In the dampest month (July) the mean dew-point is only eight-tenths of a degree below the temperature, whilst in December it sinks 10° below it. In London the dew-point is on the average 5·6° below the temperature; none of the English months are so wet as those of Sikkim, but none are so dry as the Sikkim December sometimes is.

_On the weight of the atmosphere in Sikkim; and its effects on the human frame._

Of all the phenomena of climate, the weight of the atmosphere is the most remarkable for its elusion of direct observation, when unaided by instruments. At the level of the sea, a man of ordinary bulk and stature is pressed upon by a superincumbent weight of 30,000 pounds or 13·5 tons. An inch fall or rise in the barometer shows that this load is lightened or increased, sometimes in a few hours, by nearly 1,000 pounds; and no notice is taken of it, except by the meteorologist, or by the speculative physician, seeking the subtle causes of epidemic and endemic complaints. At Dorjiling (7,400 feet), this load is reduced to less than 2,500 pounds, with no appreciable result whatever on the frame, however suddenly it be transported to that elevation. And the observation of my own habits convinced me that I took the same amount of meat, drink, sleep, exercise and work, not only without inconvenience, but without the slightest perception of my altered circumstances. On ascending to 14,000 feet, owing to the diminished supply of oxygen, exercise brings on vertigo and headache; ascending higher still, lassitude and tension across the forehead ensue, with retching, and a sense of weight dragging down the stomach, probably due to dilatation of the air contained in that organ. Such are the all but invariable effects of high elevations; varying with most persons according to the suddenness and steepness of the ascent, the amount and duration of exertion, and the length of time previously passed at great heights. After having lived for some weeks at 15,300 feet, I have thence ascended several times to 18,500, and once above 19,000 feet, without any sensations but lassitude and quickness of pulse;[417] but in these instances it required great caution to avoid painful symptoms. Residing at 15,300 feet, however, my functions were wholly undisturbed; nor could I detect any quickness of pulse or of respiration when the body was at rest, below 17,000 feet. At that elevation, after resting a party of eight men for an hour, the average of their and my pulses was above 100°, both before and after eating; in one case it was 120°, in none below 80°.

[417] I have in a note to vol. ii. p. 160, stated that I never experienced in my own person, nor saw in others, bleeding at the ears, nose, lips, or eyelids.

Not only is the frame of a transient visitor unaffected (when at rest) by the pressure being reduced from 30,000 to 13,000 pounds, but the Tibetan, born and constantly residing at upwards of 14,000 feet, differs in no respect that can be attributed to diminished pressure, from the native of the level of the sea. The averaged duration of life, and the amount of food and exercise is the same; eighty years are rarely reached by either. The Tibetan too, however inured to cold and great elevations, still suffers when he crosses passes 18,000 or 19,000 feet high, and apparently neither more nor less than I did.

Liebig remarks (in his “Animal Chemistry”) that in an equal number of respirations,[418] we consume a larger amount of oxygen at the level of the sea than on a mountain; and it can be shown that under ordinary circumstances at Dorjiling, 20·14 per cent. less is inhaled than on the plains of India. Yet the chest cannot expand so as to inspire more at once, nor is the respiration appreciably quickened; by either of which means nature would be enabled to make up the deficiency. It is true that it is difficult to count one’s own respirations, but the average is considered in a healthy man to be eighteen in a minute; in my own case it is sixteen, an acceleration of which by three or four could not have been overlooked, in the repeated trials I made at Dorjiling, and still less the eight additional inhalations required at 15,000 feet to make up for the deficiency of oxygen in the air of that elevation.

[418] For the following note I am indebted to my friend, C. Muller,
Esq., of Patna.—
According to Sir H. Davy, a man consumes 45,504 cubic inches of
oxygen in twenty-four hours, necessitating the inspiration of
147,520 cubic inches of atmospheric air.—At pressure 23 inches, and
temp. 60° this volume of atmospheric air (dry) would weigh
35,138·75 grains.—At pressure 30 in., temp. 80°, it would weigh
43,997·63 gr.
The amount of oxygen in atmospheric air is 23·32 per cent. by
weight. The oxygen, then, in 147,520 cubic inches of dry air, at
pressure 23 in., temp. 80°, weighs 8,194·35 gr.; and at pressure 30
in., temp. 80°, it weighs 10,260·25 gr.
Hence the absolute quantity of oxygen in a given volume of
atmospheric air, when the pressure is 23 in., and the temp. 60°, is
20·14 per cent. less than when the pressure is 30 in. and the temp.
80°.
When the air at pressure 23 in:, temp. 60°, is saturated with
moisture, the proportion of dry air and aqueous vapour in 100 cubic
inches is as follows:—
Dry air 97·173
Vapour 2·827
At pressure 30 in., temp. 80°, the proportions are:—
Dry air 96·133
Vapour 3·867
The effect of aqueous vapour in the air on the amount of oxygen
available for consumption, is very trifling; and it must not be
forgotten that aqueous vapour supplies oxygen to the system as well
as atmospheric air.

It has long been surmised that an alpine vegetation may owe some of its peculiarities to the diminished atmospheric pressure; and that the latter being a condition which the gardener cannot supply, he can never successfully cultivate such plants in general. I know of no foundation for this hypothesis; many plants, natives of the level of the sea in other parts of the world, and some even of the hot plains of Bengal, ascend to 12,000 and even 15,000 feet on the Himalaya, unaffected by the diminished pressure. Any number of species from low countries may be cultivated, and some have been for ages, at 10,000 to 14,000 feet without change. It is the same with the lower animals; innumerable instances may with ease be adduced of pressure alone inducing no appreciable change, whilst there is absence of proof to the contrary. The phenomena that accompany diminished pressure are the real obstacles to the cultivation of alpine plants, of which cold and the excessive climate are perhaps the most formidable. Plants that grow in localities marked by sudden extremes of heat and cold, are always very variable in stature, habit, and foliage. In a state of nature we say the plants “accommodate themselves” to these changes, and so they do within certain limits; but for one that survives of all the seeds that germinate in these inhospitable localities, thousands die. In our gardens we can neither imitate the conditions of an alpine climate, nor offer others suited to the plants of such climates.

The mean height of the barometer at Mr. Hodgson’s was 23·010, but varied 0·161 between July, when it was lowest, and October, when it was highest; following the monthly rise and fall of Calcutta as to period, but not as to amount (or amplitude); for the mercury at Calcutta stands in July upwards of half an inch (0·555 Prinsep) lower than it does in December.

The diurnal tide of atmosphere is as constant as to the time of its ebb and flow at Dorjiling as at Calcutta; and a number of very careful observations (made with special reference to this object) between the level of the plains of India, and 17,000 feet, would indicate that there is no very material deviation from this at any elevation in Sikkim. These times are very nearly 9.50 a.m. and about 10 p.m. for the maxima, the 9.50 a.m. very constantly, and the 10 p.m. with more uncertainty; and 4 a.m. and 4 p.m. for the minima, the afternoon ebb being most true to its time, except during the rains.

At 9.50 a.m. the barometer is at its highest, and falls till 4 p.m., when it stands on the average of the year 0·074 of an inch lower; during the same period the Calcutta fall is upwards of one-tenth of an inch (0·121 Prinsep).

It has been proved that at considerable elevations in Europe, the hours of periodic ebb and flow differ materially from those which prevail at the level of the sea; but this is certainly not the case in the Sikkim Himalaya.

The amplitude decreases in amount from 0·100 at the foot of the hills, to 0·074 at 7000 feet; and the mean of 132 selected unexceptionable observations, taken at nine stations between 8000 and 15,500 feet, at 9.50 a.m. and 4 p.m., gives an average fall of 0·056 of an inch; a result which is confirmed by interpolation from numerous horary observations at these and many other elevations, where I could observe at the critical hours.

That the Calcutta amplitude is not exceptionally great, is shewn by the register kept at different places in the Gangetic valley and plains of India, between Saharunpore and the Bay of Bengal. I have seen apparently trustworthy records of seven[419] such, and find that in all it amounts to between 0·084 and 0·120 inch, the mean of the whole being 0·101 of an inch.

[419] Calcutta, Berampore, Benares, Nagpore, Moozufferpore, Delhi, and Saharunpore.

The amplitude is greatest (0·088) in the spring months (March, April, and May), both at Dorjiling and Calcutta: it is least at both in June and July, (0·027 at Dorjiling), and rises again in autumn (to ·082 in September).

The horary oscillations also are as remarkably uniform at all elevations, as the period of ebb and flow: the mercury falls slowly from 9.50 a.m. (when it is at its highest) till noon, then rapidly till 3 p.m., and slowly again till 4 p.m.; after which there is little change until sunset; it rises rapidly between 7 and 9 p.m., and a little more till 10 p.m.; thence till 4 a.m. the fall is inconsiderable, and the great rise occurs between 7 and 9 a.m.

It is well known that these fluctuations of the barometer are due to the expansion and contraction by heat and moisture of the column of atmosphere that presses on the mercury, in the cistern of the instrument: were the air dry, the effect would be a single rise and fall;[420] the barometer would stand highest at the hottest of the twenty-four hours, and lowest at the coldest; and such is the case in arid continental regions which are perennially dry. That such would also be the case at Calcutta and throughout the Himalaya of Sikkim, is theoretically self-evident, and proved by my horary observations taken during the rainy months of 1848. An inspection of these at the end of this section (where a column contains the pressure of dry air) shows but one maximum of pressure, which occurs at the coldest time of the twenty-four hours (early in the morning), and one minimum in the afternoon. In the table of mean temperatures of the months, also appended to this section, will also be found a column allowing the pressure of dry air, whence it will be seen that there is but one maximum of the pressure of dry air, occurring at the coldest season in December, and one minimum, in July. The effect of the vapour is the same on the annual as upon the diurnal march of the pressure, producing a double maximum and minimum in the year in one case, and in the twenty-four hours in the other.

[420] This law, for which we are indebted to Professor Dove, has been clearly explained by Colonel Sabine in the appendix to his translation of Humboldt’s “Cosmos,” vol. i. p. 457.

I append a meteorological register of the separate months, but at the same time must remind the reader that it does not pretend to strict accuracy. It is founded upon observations made at Dorjiling by Dr. Chapman in the year 1837, for pressure temperature and wet-bulb only; the other data and some modifications of the above are supplied from observations of my own. Those for terrestrial and nocturnal radiation are accurate as far as they go, that is to say, they are absolute temperatures taken by myself, which may, I believe, be recorded in any year, but much higher are no doubt often to be obtained. The dew-points and saturations are generally calculated from the mean of two day observations (10 a.m. and 4 p.m.) of the wet-bulb thermometer, together with the minimum, or are taken from observations of Daniell’s hygrometer; and as I find the mean of the temperature of 10 a.m., 4 p.m., and the minimum, to coincide within a few tenths with the mean temperature of the whole day, I assume that the mean of the wet-bulb observations of the same hours will give a near approach to that of the twenty-four hours. The climate of Dorjiling station has been in some degree altered by extensive clearances of forest, which render it more variable, more exposed to night frosts and strong sun-heat, and to drought, the drying up of small streams being one direct consequence. My own observations were taken at Mr. Hodgson’s house, elevated 7,430 feet, the position of which I have indicated at the commencement of this section, where the differences of climate due to local causes are sufficiently indicated to show that in no two spots could similar meteorological results be obtained. At Mr. Hodgson’s, for instance, the uniformity of temperature and humidity is infinitely more remarkable than at Dr. Chapman’s, possibly from my guarding more effectually against radiation, and from the greater forests about Mr. Hodgson’s house. I have not, however, ventured to interfere with the temperature columns on this account.

DORJILING METEOROLOGICAL REGISTER.

Jan. Feb. Mar. Apr. May June Pressure of Atmosphere[421] Range of Pressure Mean Shade Maximum Shade Maximum Sun Greatest Difference Mean Maximum Shade Minimum Shade Minimum Radiation Greatest Difference Mean Minimum Shade Mean Daily Range of Temps Sunk Thermometer Mean Dew-point Mean Dryness Force of Vapour Pressure of Dry Air Mean Saturation Rain in inches 23·307 ·072 40·0 56·0 119·0 72·0 47·2 29·0 16·0 12·7 32·8 14·4 46·0 34·3 5·1 ·216 23·091 ·84 1·72 23·305 ·061 42·1 57·0 124·0 78·0 50·0 25·5 23·0 15·3 34·2 15·8 48·0 37·2 3·9 ·239 23·066 ·87 0·92 23·307 ·083 50·7 66·5 120·0 60·0 58·4 37·0 27·8 8·7 43·1 15·3 50·0 45·8 5·8 ·323 23·084 ·82 1·12 23·280 ·085 55·9 68·5 125·0 66·0 63·7 38·0 33·0 16·0 48·1 15·6 58·0 49·8 6·6 ·371 22·909 ·80 2·52 23·259 ·088 57·6 69·0 125·0 65·0 65·3 38·0 40·0 10·0 50·0 15·3 61·0 54·4 2·7 ·434 22·825 ·91 9·25 23·207 ·067 61·2 71·0 126·2 62·2 66·7 51·5 47·0 4·8 55·8 10·9 62·0 59·5 2·0 ·515 22·692 ·93 26·96

July Aug. Sept. Oct. Nov. Dec. Mean Pressure of Atmosphere[421] Range of Pressure Mean Shade Maximum Shade Maximum Sun Greatest Difference Mean Maximum Shade Minimum Shade Minimum Radiation Greatest Difference Mean Minimum Shade Mean Daily Range of Temps Sunk Thermometer Mean Dew-point Mean Dryness Force of Vapour Pressure of Dry Air Mean Saturation

Rain in inches 23·203 ·062 61·4 69·5 130·0 62·0 65·5 56·0 52·0 3·5 57·3 8·2 62·2 60·7 0·8 ·535 22·668 ·97

25·34 23·230 ·070 61·7 70·0 133·0 62·0 66·1 54·5 50·0 3·5 57·4 8·7 62·0 60·4 1·1 ·530 22·700 ·96

29·45 23·300 ·082 59·9 70·0 142·0 70·0 64·7 51·5 47·5 10·0 55·2 9·5 61·0 58·5 1·4 ·498 22·802 ·95

15·76 23·372 ·075 58·0 68·0 133·0 65·0 66·5 43·5 32·0 12·0 49·5 17·0 60·0 52·5 4·2 ·407 22·865 ·86

8·66 23·330 ·078 50·0 63·0 123·0 68·0 56·5 38·0 30·0 12·0 43·5 13·0 55·0 46·5 3·2 ·331 22·999 ·90

0·11 23·365 ·062 43·0 56·0 108·0 77·2 51·6 32·5 26·0 10·0 34·9 16·7 49·0 31·8 10·6 ·198 23·165 ·69

0·45 22·289 ·074 53·5 65·4 125·7 67·3 60·2 41·3 35·4 9·9 46·8 13·4 56·2 49·4 4·0 ·383 22·906 ·88 Sum 122·26

[421] These are taken from Dr. Chapman’s Table; and present a greater annual range (=0·169) than my observations in 1848–9, taken at Mr. Hodgson’s which is higher than Dr. Chapman’s; or than Mr. Muller’s, which is a little lower, and very near it.

_Horary Observations at Jillapahar, Dorjiling, Alt. 7,430 feet._

JULY, 1848

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air 7 23 27 22 20 26 12 11 25 23 13 10 6 6 22 6 6 19 1 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 22·877 ·882 ·884 +·899 ·899 ·884 ·876 ·866 ·852 ·846 –·840 ·845 ·853 ·867 ·878 ·885 +·887 ·887 59·6 62·1 62·6 63·5 64·1 65·0 64·1 64·4 64·8 64·1 64·7 63·7 62·7 61·0 60·7 60·5 60·2 59·8 58·9 60·6 61·3 61·7 62·3 63·1 61·7 61·0 62·6 61·7 64·0 61·5 61·1 59·5 59·4 59·5 59·2 59·1 0·7 1·5 1·3 1·8 1·8 1·9 2·4 3·4 2·2 2·4 0·7 2·2 1·6 1·5 1·3 1·0 1·0 0·7 ·504 ·534 ·546 ·554 ·565 ·580 ·566 ·541 ·571 ·554 ·597 ·549 ·542 ·515 ·512 ·514 ·508 ·507 5·65 6·03 6·10 6·12 6·27 6·44 6·13 6·00 6·32 6·13 6·62 6·12 6·03 5·74 5·72 5·75 5·70 5·68 ·988 ·950 ·960 ·945 ·945 ·940 ·923 ·892 ·930 ·924 ·978 ·928 ·948 ·952 ·960 ·968 ·965 ·975 22·373 ·348 ·338 ·345 ·334 ·304 ·310 ·325 ·281 ·292 –·243 ·296 ·311 ·352 ·366 ·371 ·379 +·382

AUGUST

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air 15 26 28 28 24 23 21 21 21 19 19 19 19 19 19 19 19 19 1 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 22·909 ·904 ·915 +·917 ·915 ·905 ·898 ·884 ·873 ·855 –·853 ·863 ·865 ·878 ·890 +·893 ·892 ·889 59·8 62·1 63·1 64·3 64·7 64·7 65·3 65·0 64·8 63·9 63·2 62·3 61·6 61·1 60·7 60·3 60·1 60·0 59·5 61·5 61·9 62·7 63·1 63·4 63·3 63·4 63·1 62·4 61·7 60·8 60·4 60·2 60·0 59·7 59·7 59·4 0·3 0·6 1·2 1·6 1·6 1·3 2·0 1·6 1·7 1·5 1·5 1·5 1·2 0·9 0·7 0·6 0·4 0·6 ·514 ·549 ·558 ·572 ·580 ·586 ·584 ·586 ·579 ·568 ·554 ·538 ·531 ·527 ·523 ·518 ·517 ·513 5·70 6·13 6·20 6·35 6·42 6·50 6·48 6·50 6·43 6·30 6·15 6·00 5·92 5·88 5·85 5·78 5·79 5·73 ·992 ·980 ·962 ·950 ·948 ·958 ·940 ·950 ·943 ·952 ·952 ·952 ·962 ·970 ·976 ·980 ·988 ·980 +22·395 ·355 ·357 ·345 ·335 ·319 ·314 ·298 ·294 –·287 ·299 ·325 ·334 ·351 ·367 ·375 ·375 ·376

SEPTEMBER

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air 28 29 28 24 23 23 23 23 23 19 19 20 21 22 24 24 23 8 a.m. 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 23·000 ·013 +·018 ·009 22·995 ·980 ·962 ·947 –·944 ·944 ·948 ·958 ·975 ·986 +·991 ·989 ·994 59·2 60·1 60·8 61·6 62·4 62·7 62·8 62·3 61·8 60·3 59·4 58·7 58·2 57·8 57·4 57·0 56·7 58·1 58·5 59·5 60·0 60·5 60·5 60·4 60·0 59·9 58·6 58·4 57·4 57·0 56·6 56·4 55·9 55·4 1·1 1·6 1·3 1·6 1·9 2·2 2·4 2·3 1·9 1·7 1·0 1·3 1·2 1·2 1·0 1·1 1·3 ·492 ·497 ·514 ·523 ·533 ·532 ·531 ·522 ·521 ·498 ·496 ·479 ·473 ·467 ·463 ·456 ·449 5·50 5·57 5·77 5·83 5·93 5·92 5·90 5·83 5·82 5·58 5·58 5·60 5·33 5·25 5·23 5·15 5·07 ·968 ·945 ·958 ·950 ·942 ·942 ·925 ·924 ·940 ·940 ·968 ·960 ·962 ·960 ·968 ·962 ·927 22·508 ·526 ·504 ·506 ·462 ·448 ·431 ·425 –·423 ·446 ·452 ·479 ·502 ·519 ·528 ·533 +·545

OCTOBER (22 days)

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air 11 19 20 20 19 13 15 13 13 14 16 13 6 7 3 7 14 18 14 6-6.30 7 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 23·066 ·072 ·086 ·099 +·100 ·079 ·072 ·055 ·033 ·027 ·024 –·022 ·033 ·045 ·038 ·061 +·072 ·067 ·068 54·4 54·3 55·2 56·3 57·1 57·6 57·9 58·0 57·7 57·9 57·9 56·6 55·9 55·4 53·7 55·1 54·6 54·5 54·1 52·7 52·3 53·7 54·4 55·5 55·6 56·1 56·4 56·6 56·2 56·1 54·8 54·4 53·8 53·3 54·1 53·0 53·0 52·8 1·7 2·0 1·5 1·9 1·6 2·0 1·8 1·6 1·1 1·7 1·8 1·8 1·5 1·6 0·4 1·0 1·6 1·5 1·3 ·409 ·403 ·423 ·434 ·450 ·451 ·459 ·463 ·466 ·460 ·458 ·439 ·433 ·424 ·417 ·429 ·413 ·413 ·411 4·65 4·58 4·78 4·90 5·07 5·08 5·15 5·17 5·25 5·16 5·15 4·98 4·90 4·80 4·75 4·83 4·82 4·82 4·65 ·943 ·025 ·950 ·935 ·942 ·935 ·940 ·950 ·962 ·940 ·940 ·948 ·950 ·950 ·990 ·965 ·949 ·950 ·962 22·657 +·669 ·663 ·665 ·650 ·728 ·613 ·592 ·567 ·567 ·–·566 ·583 ·600 ·621 ·621 ·632 ·659 ·654 ·657

G.

ON THE RELATIVE HUMIDITY, AND ABSOLUTE AMOUNT OF VAPOUR CONTAINED IN THE ATMOSPHERE AT DIFFERENT ELEVATIONS IN THE SIKKIM HIMALAYA.

My observations for temperature and wet-bulb being for the most part desultory, taken at different dates, and under very different conditions of exposure, etc., it is obvious that those at one station are hardly, if at all, comparative with those of another, and I have therefore selected only such as were taken at the same date and hour with others taken at the Calcutta Observatory, or as can easily be reduced; which thus afford a standard (however defective in many respects) for a comparison. I need hardly remind my reader that the vapour-charged wind of Sikkim is the southerly one, which blows over Calcutta; that in its passage northwards to Sikkim in the summer months, it traverses the heated plains at the foot of the Himalaya, and ascending that range, it discharges the greater part of its moisture (120 to 140 inches annually) over the outer Himalayan ranges, at elevations of 4000 to 8000 feet. The cooling effect of the uniform covering of forest on the Sikkim ranges is particularly favourable to this deposition, but the slope of the mountains being gradual, the ascending currents are not arrested and cooled so suddenly as in the Khasia mountains, where the discharge is consequently much greater. The heating of the atmosphere, too, over the dry plains at the foot of the outer range, increases farther its capacity for the retention of vapour, and also tends to render the rain-fall less sudden and violent than on the Khasia, where the south wind blows over the cool expanse of the Jheels. It will be seen from the following observations, that in Sikkim the relative humidity of the atmosphere remains pretty constantly very high in the summer months, and at all elevations, except in the rearward valleys; and even there a humid atmosphere prevails up to 14,000 feet, everywhere within the influence of the snowy mountains. The uniformly high temperature which prevails throughout the summer, even at elevations of 17,000 and 18,000 feet, is no doubt proximately due to the evolution of heat during the condensation of these vapours. It will be seen by the pages of my journal, that continued sunshine, and the consequent heating of the soil, is almost unknown during the summer, at any elevation on the outer or southward ranges of Dorjiling: but the sunk thermometer proves that in advancing northward into the heart of the mountains and ascending, the sun’s effect is increased, the temperature of the earth becoming in summer considerably higher than that of the air. With regard to the observations themselves, they may be depended upon as comparable with those of Calcutta, the instruments having been carefully compared, and the cases of interpolation being few. The number of observations taken at each station is recorded in a separate column; where only one is thus recorded, it is not to be regarded as a single reading, but the mean, of several taken during an hour or longer period. I have rejected all solitary observations, even when accompanied by others at Calcutta; and sundry that were, for obvious reasons, likely to mislead. Where many observations were taken at one place, I have divided them into sets, corresponding to the hours at which alone the Calcutta temperature and wet-bulb thermometer are recorded,[423] in order that meteorologists may apply them to the solution of other questions relating to the distribution of heat and moisture. The Dorjiling observations, and those in the immediate neighbourhood of that station, appeared to me sufficiently numerous to render it worth while classing them in months, and keeping them in a series by themselves. The tensions of vapour are worked from the wet-bulb readings by Apjohn’s formula and tables, corrected for the height of the barometer at the time. The observations, except where otherwise noted, are taken by myself.

[423] Sunrise; 9.50 a.m.; noon; 2.40 p.m.; 4 p.m., and sunset.

SERIES I. _Observations made at or near Dorjiling._

JANUARY, 1849

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 15 15 10 8 9 The Dale,[424] Mr. Muller’s … … … 6956 … … … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset 42·9 45·8 48·3 48·6 46·5 32·4 33·8 37·4 37·8 37·1 10·5 12·0 10·9 10·8 9·4 ·202 ·212 ·241 ·244 ·238 67·5 72·9 76·1 75·1 71·8 55·3 55·7 55·1 54·8 54·9 12·2 17·2 21·0 20·3 16·9 ·446 ·455 ·444 ·440 ·441 57 … … Mean 46·4 35·7 10·7 ·227 72·7 55·2 17·5 ·445

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·700 2·63 gr. 0·562 4·86 gr.

[424] Observations were taken by Mr. Muller.

JANUARY, 1850

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 3 6 3 5 5 5 13 4

1 Jillapahar, Mr. Hodgson’s … … … … … Saddle of road at Sinchul Pacheem 7430 … … … … … … 7412

7258 Sunrise 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Miscel. Do.

Do. 32·8 39·5 42·4 41·9 41·1 38·7 41·9 41·1

39·8 30·1 34·7 38·0 37·8 38·5 35·6 39·9 36·4

38·7 2·7 4·8 4·4 4·1 2·6 3·1 2·0 4·7

1·1 ·186 ·219 ·246 ·244 ·250 ·226 ·263 ·233

·252 51·5 66·9 74·1 78·3 77·4 72·4 77·9 67·7

71·6 48·5 55·1 51·7 51·4 59·5 54·7 60·1 57·2

50·5 3·0 11·8 22·4 26·9 17·9 17·7 17·8 10·5

21·1 ·354 ·444 ·395 ·391 ·514 ·438 ·525 ·476

·379 45 … … Mean 39·9 36·6 3·3 ·235 70·9 54·3 16·6 ·435

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·890 2·75 gr. 0·580 4·86 gr.

FEBRUARY, 1850

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 6 18 12 12 17 19 13 Jillapahar … … … … … The Dale[425] 7430 … … … … … 6956 Sunrise 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Misc. 36·9 42·9 44·8 44·8 44·0 42·4 40·8 34·7 38·6 41·3 37·4 35·6 35·8 35·1 2·2 4·3 3·5 7·4 8·4 6·6 5·7 ·219 ·251 ·276 ·241 ·226 ·228 ·222 60·0 72·8 79·8 82·4 81·1 76·3 69·9 54·2 58·8 58·7 57·9 58·1 60·7 59·8 5·8 14·0 21·1 24·5 23·0 15·6 10·1 ·431 ·503 ·501 ·487 ·492 ·536 ·518 97 … … Mean 42·4 36·9 5·4 ·238 74·6 58·3 16·3 ·495

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·828 2·75 gr. 0·590 5·40 gr.

[425] Observations were taken by Mr. Muller.

MARCH, 1850

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 10 8 5 8 6 3 Jillapahar … … … … Pacheem 7430 … … … … 7258 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Miscel. 44·2 45·5 46·4 45·5 43·1 44·8 42·7 43·0 44·0 43·4 41·5 44·6 1·5 2·5 2·4 2·1 1·6 0·2 ·290 ·293 ·303 ·297 ·278 ·310 81·6 88·2 91·3 90·1 82·9 85·0 64·1 57·0 53·2 52·0 63·7 74·8 17·5 31·2 38·1 38·1 19·2 10·2 ·602 ·472 ·416 ·399 ·590 ·848 40 … … Mean 44·9 43·2 1·7 ·295 86·5 60·8 25·7 ·555

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·940 3·42 gr. 0·438 5·72 gr.

APRIL

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 3 3 1 7 2 4 3 Jillapahar, 1849 … … Dr. Campbell’s, 1850 … … … 7430 … … 6932 … … … 9.50 a.m. Noon 2.40 p.m. 9.50 a.m. Noon 4 p.m. 57·0 59·8 60·2 61·8 65·4 57·5 56·9 40·2 44·1 44·4 53·3 52·8 53·7 51·4 16·8 15·7 15·8 8·5 12·6 3·8 5·5 ·266 ·305 ·308 ·417 ·411 ·423 ·392 90·3 97·0 97·7 86·7 91·3 88·6 82·8 71·3 64·5 73·4 66·3 68·8 72·1 73·0 19·0 32·5 24·3 20·4 22·5 16·5 9·8 ·758 ·607 ·812 ·644 ·699 ·778 ·800 23 … … Mean 59·8 48·6 11·3 ·360 90·6 69·9 20·7 ·728

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·684 3·98 gr. 0·523 7·65 gr.

MAY

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 3 45 Smith’s Hotel, 1848 Colinton,[426] 1849 6863 7179 Miscel. Miscel. 57·2 60·4 55·0 57·9 2·2 1·5 ·443 ·466 88·6 90·0 78·4 77·2 10·2 12·8 ·951 ·917 48 … Mean 58·8 56·5 2·4 ·455 89·3 77·8 11·5 ·934

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·926 5·22 gr. 0·698 9·90 gr.

[426] Observations were taken by Mr. Muller.

JUNE

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 40 Colinton,[427] 7179 Miscel. 60·9 57·6 3·3 ·483 85·5 78·4 7·1 ·952

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·895 5·39 gr. 0·800 10·17 gr.

[427] Observations were taken by Mr. Muller.

JULY, 1848

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 18 25 24 16 31 31 31 Jillapahar … … … The Dale,[428] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 63·2 65·0 64·7 63·8 60·2 66·3 63·0 61·4 62·6 62·3 61·5 58·7 63·3 60·9 1·8 2·4 2·4 2·3 1·5 3·0 2·1 ·548 ·570 ·565 ·550 ·537 ·621 ·575 87·0 89·0 88·1 87·2 81·3 88·0 84·8 79·4 80·0 79·4 79·5 79·0 79·6 79·2 7·6 9·0 8·7 7·7 2·3 8·4 5·6 ·983 1·001 ·983 ·985 ·969 ·989 ·977 176 … … Mean 63·7 61·5 2·2 ·567 86·5 79·4 7·0 ·984

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·929 6·06 gr. 0·800 10·45 gr.

[428] Observations were taken by Mr. Muller.

AUGUST, 1848

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 23 21 17 13 31 31 31 Jillapahar … … … The Dale,[429] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 64·2 64·7 64·7 63·9 60·5 65·3 62·8 62·4 63·3 62·8 62·5 59·5 63·6 61·8 1·8 1·4 1·9 1·4 1·0 1·7 1·0 ·567 ·584 ·574 ·568 ·551 ·628 ·591 85·8 87·2 87·4 86·5 80·8 87·2 83·7 79·1 79·2 79·3 79·5 78·8 79·2 78·7 6·7 8·0 8·1 7·0 2·0 8·0 5·0 ·973 ·976 ·979 ·984 ·962 ·976 ·959 167 … … Mean 63·7 62·3 1·5 ·580 85·5 79·1 6·4 ·973

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·995 6·25 gr. 0·818 10·35 gr.

[429] Observations were taken by Mr. Muller.

SEPTEMBER, 1848

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 28 23 23 21 30 30 30 Jillapahar … … … The Dale,[430] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 60·8 62·4 62·4 62·0 57·4 64·9 60·8 59·3 60·3 59·6 59·6 56·2 60·8 59·0 1·5 2·1 2·8 2·4 1·2 4·1 1·8 ·511 ·528 ·516 ·516 ·495 ·573 ·543 87·0 88·5 88·1 86·9 80·9 88·8 84·7 78·4 78·1 77·4 77·1 78·3 77·4 76·6 8·6 10·4 10·7 9·8 2·6 11·4 8·1 ·952 ·943 ·922 ·914 ·948 ·923 ·899 185 … … Mean 61·5 59·3 2·3 ·526 86·4 77·6 8·8 ·929

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·932 5·72 gr. 0·760 9·88 gr.

[430] Observations were taken by Mr. Muller.

OCTOBER, 1848

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 6 6 6 4 8 8 17 19 Jillapahar … … Goong. Ditto The Dale,[431] … … 7430 … … 7436 7441 6952 … … Noon 2.40 p.m. 4 p.m. Misc. Misc. 6 a.m. 2 p.m. 6 p.m. 55·9 55·7 55·6 48·3 51·2 55·2 61·4 56·9 55·3 54·9 54·9 48·3 50·2 52·7 56·3 54·2 0·6 0·8 0·7 0 1·0 2·5 5·1 2·7 ·446 ·440 ·441 ·352 ·376 ·439 ·497 ·463 84·4 86·0 85·2 81·2 80·7 76·1 87·0 82·8 75·3 73·3 74·4 73·7 66·9 74·2 71·2 73·9 9·1 12·7 10·8 7·5 13·8 1·9 15·8 8·9 ·863 ·808 ·837 ·819 ·657 ·834 ·756 ·824 74 … … Mean 55·0 53·4 1·7 ·432 82·9 72·9 10·1 ·800

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·950 4·74 gr. 0·658 8·55 gr.

[431] Observations were taken by Mr. Muller.

NOVEMBER AND DECEMBER, 1848

DORJILING CALCUTTA No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 4 8 6 9 19 The Dale[432] Nov./Dec. … December … 6952 … … … … 6 a.m. 2 p.m. 6 p.m. 2 p.m. 6 a.m. 45·6 60·0 50·6 49·7 44·0 41·4 48·3 44·7 41·7 40·5 4·2 11·7 5·9 8·0 3·5 ·277 ·355 ·311 ·280 ·269 67·9 83·3 77·3 79·3 75·8 64·7 65·2 63·1 59·0 62·6 3·2 18·1 14·2 20·3 13·2 ·610 ·621 ·579 ·505 ·569 46 … … Mean 49·9 43·3 6·7 ·298 76·7 62·9 13·8 ·577

Dorjiling Calcutta Humidity Vapour in cubic foot of atmosphere 0·798 3·40 gr. 0·640 6·27 gr.

[432] Observations were taken by Mr. Muller.

_Comparison of Dorjiling and Calcutta._

HUMIDITY WEIGHT OF VAPOUR IN CUBIC FOOT OF AIR No. of Obs. Month Dorjiling Calcutta Diff. Dorjiling Dorjiling Calcutta Diff. Calcutta 102 97 40 23 48 40 176 167 185 74 46 January February March April May June July August September October Nov. and Dec. –·795 ·828 ·940 ·684 ·926 ·895 ·929 +·955 ·932 ·950 ·798 ·572 ·590 –·438 ·523 ·698 ·800 ·800 +·818 ·760 ·658 ·640 +·224 +·238 +·502 +·161 +·228 +·095 +·129 +·136 +·172 +·292 +·158 –2·68 2·75 3·42 3·98 5·22 5·39 6·06 +6·25 5·72 4·74 6·27 –4.80 5·40 5·72 7·65 9·90 10·17 10·05 +10·35 9·88 8·55 6·27 +2·12 +2·65 +2·30 +3·67 +4·62 +4·78 +3·99 +4·10 +4·16 +3·81 +2·87 998 Mean 0·876 0·663 +·212 4·51 8·07 +3·55

It is hence evident, from nearly 1000 comparative observations, that the atmosphere is relatively more humid at Dorjiling than at Calcutta, throughout the year. As the southerly current, to which alone is due all the moisture of Sikkim, traverses 200 miles of land, and discharges from sixty to eighty inches of rain before arriving at Dorjiling, it follows that the whole atmospheric column is relatively drier over the Himalaya than over Calcutta; that the absolute amount of vapour, in short, is less than it would otherwise be at the elevation of Dorjiling, though the relative humidity is so great. A glance at the table at the end of this section appears to confirm this; for it is there shown that, at the base of the Himalaya, at an elevation of only 250 feet higher than Calcutta, the absolute amount of vapour is less, and of relative humidity greater, than at Calcutta.

SERIES II. _Observations at various Stations and Elevations in the Himalaya of East Nepal and Sikkim._

ELEVATION 735 TO 2000 FEET

EAST NEPAL AND SIKKIM CALCUTTA No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 3 2 1 3 1 6 1 5 5 11

10 Katong Ghat, Teesta river Great Rungeet, at bridge Ditto Tambur river, E. Nepal Ditto Bhomsong, Teesta river Ditto Little Rungeet Pemiongchi, Great Rungeet Punkabaree Ditto Guard house (Gt. Rungeet) 735 818 818 1388 1457 1596 1596 1672 1840 1850 1850 1864 Dec. April May Nov. Nov. Dec. May Jan. Dec. March May April 60·2 82·8 77·8 60·6 64·2 58·6 68·2 51·0 54·6 70·1 73·5 73·7 55·3 63·5 60·3 57·0 59·1 52·0 66·4 50·2 53·7 55·6 68·3 63·8 4·9 19·3 17·5 3·6 5·1 6·6 1·8 0·8 0·9 14·5 5·2 9·9 ·447 ·588 ·528 ·473 ·507 ·399 ·647 ·377 ·424 ·472 ·687 ·592 73·2 95·8 91·7 73·3 77·3 71·6 82·6 58·5 73·5 79·2 83·7 92·4 56·7 61·9 78·3 62·7 63·4 57·0 77·4 58·0 66·2 62·6 77·9 67·0 16·5 33·9 13·4 10·6 13·9 14·6 5·2 0·5 7·3 16·6 5·8 25·4 ·468 ·557 ·947 ·571 ·585 ·474 ·923 ·489 ·642 ·570 ·938 ·660 48 Mean 66·3 58·8 7·5 ·512 79·4 65·8 13·6 ·652

East Nepal and Sikkim Calcutta Humidity Weight of vapour 0·717 5·57 gr. 0·663 6·88 gr.

ELEVATION 2000 TO 3000 FEET

EAST NEPAL AND SIKKIM CALCUTTA No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 2 8 3 3 2 8 12 8 3 Singdong Mywa Guola, E. Nepal Pemmi river, E. Nepal Tambur river, E. Nepal Blingbong (Teesta) Lingo (Teesta) Serriomsa (Teesta) Lingmo (Teesta) Ditto 2116 2132 2256 2545 2684 2782 2820 2849 2952 Dec. Nov. Nov. Nov. May May Dec. May Dec. 60·5 66·2 55·6 57·3 72·6 75·8 64·1 68·6 56·4 53·4 57·5 53·9 51·6 64·0 67·3 56·8 64·6 53·5 7·1 8·7 1·7 5·7 8·6 8·5 7·3 4·0 2·9 ·419 ·481 ·426 ·394 ·597 ·666 ·469 ·610 ·420 72·1 75·7 62·9 75·0 81·7 90·7 70·8 87·9 69·5 52·9 68·7 62·3 63·7 73·6 77·7 62·4 74·9 66·5 19·2 7·0 0·6 11·3 8·1 13·0 8·4 13·0 3·0 ·411 ·697 ·566 ·591 ·817 ·932 ·567 ·851 ·647 49 Mean 64·1 58·1 6·1 ·498 76·3 67·0 9·3 ·675

East Nepal and Sikkim Calcutta Humidity Weight of vapour 0·820 5·45 gr. 0·740 7·13 gr.

ELEVATION 3000 TO 4000 FEET

EAST NEPAL AND SIKKIM CALCUTTA No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 5 9 3 2 2 7 7 1 3 1 1 2 5 Kulhait river Ratong river Tambur river Chingtam Tikbotang Myong Valley Iwa river Ratong river Tukcham Pacheem village Yankoong Mikk Sunnook 3159 3171 3201 3404 3763 3782 3783 3790 3849 3855 3867 3912 3986 Jan. Jan. Nov. Nov. Dec. Oct. Dec. Jan. Nov. Jan. Dec. May Dec. 49·8 44·2 53·0 54·8 56·5 61·4 47·5 56·2 68·8 54·5 50·0 66·1 47·9 47·0 43·0 50·0 49·0 53·4 58·4 45·6 41·1 65·4 46·3 43·6 63·9 45·5 2·8 1·2 3·0 5·8 3·1 3·0 1·9 15·1 3·4 8·2 6·4 2·2 2·4 ·337 ·294 ·373 ·360 ·419 ·496 ·321 ·275 ·625 ·329 ·299 ·595 ·320 65·8 69·9 72·9 74·9 68·0 80·7 73·3 75·8 83·7 73·6 69·1 84·3 69·4 57·3 56·6 63·2 73·0 61·8 71·2 64·7 53·0 76·8 59·4 63·8 75·1 61·1 8·5 13·3 9·7 1·9 6·2 9·5 8·6 22·8 6·9 14·2 5·3 9·2 8·3 ·477 ·466 ·582 ·802 ·555 ·755 ·611 ·414 ·904 ·513 ·593 ·856 ·542 48 Mean 54·7 50·2 4·5 ·388 74·0 64·4 9·6 ·621

East Nepal and Sikkim Calcutta Humidity Weight of vapour 0·858 4·23 gr. 0·732 6·60 gr.

ELEVATION 4000 TO 5000 FEET

EAST NEPAL AND SIKKIM CALCUTTA No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens. 3 4 2 3 7 3 6 7 10 5 5 2 16 6 4 4 2 4 7 6 3 6 11 9 Yangyading Gorh Namgah Taptiatok (Tambur) Myong Valley Jummanoo Nampok Chakoong Singtam Namten Purmiokshong Rungniok Singtam Cheadam Sablakoo Bheti Temi Lingtam Khersiong Ditto Tassiding Lingcham Dikkeeling Tchonpong 4111 4128 4229 4283 4345 4362 4377 4407 4426 4483 4521 4565 4575 4653 4676 4683 4771 4805 4813 4813 4840 4870 4952 4978 Dec. May Oct. Nov. Oct. Nov. Dec. May May Dec. Nov. Jan. Oct/Nov. Dec. Dec. Nov. May May Jan. Mar. Dec. Dec. Dec. Jan. 52·0 66·4 57·2 51·3 59·1 60·4 49·6 57·8 62·4 44·7 60·5 54·7 63·8 51·4 50·1 59·0 59·8 60·4 51·0 53·6 52·0 48·5 62·0 49·4 43·6 59·0 54·1 45·8 57·8 50·0 49·1 57·6 61·7 44·3 56·5 44·3 60·1 46·6 44·9 52·3 50·1 56·6 45·2 45·5 46·6 46·1 55·3 34·7 8·4 7·4 3·1 5·5 1·3 10·4 0·5 0·2 0·7 0·4 4·0 10·4 3·7 4·8 5·2 6·7 9·7 3·8 5·8 8·1 5·4 2·4 6·7 14·7 ·300 ·506 ·429 ·323 ·487 ·374 ·362 ·483 ·553 ·307 ·466 ·307 ·525 ·332 ·314 ·405 ·374 ·467 ·316 ·320 ·333 ·327 ·447 ·219 71·1 85·5 80·8 73·3 81·7 77·4 64·1 83·9 88·6 64·8 79·2 66·5 82·5 70·2 72·9 78·3 81·2 80·0 67·0 77·1 79·7 78·5 80·8 71·0 67·2 74·2 73·7 64·8 72·9 70·2 56·3 76·2 79·0 58·3 69·5 59·7 76·7 55·0 65·7 66·1 74·1 73·8 49·8 70·5 60·8 71·8 62·0 54·7 3·9 11·3 7·1 8·5 8·8 7·2 7·8 7·7 9·6 6·5 9·7 6·8 5·8 15·2 7·2 12·2 7·1 6·2 17·2 6·6 18·9 6·7 18·8 16·3 ·663 ·834 ·819 ·614 ·797 ·731 ·462 ·889 ·969 ·495 ·715 ·517 ·901 ·442 ·632 ·639 ·834 ·820 ·370 ·738 ·538 ·771 ·559 ·439 137 Mean 55·7 50·4 5·4 ·387 76·5 66·8 9·7 ·675

East Nepal and Sikkim Calcutta Humidity Weight of vapour 0·837 4·33 gr. 0·730 7·12 gr.

ELEVATION 5000 TO 6000 FEET