| 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 |
| 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.