Himalayan Journals Part 44

The difference of temperature between Calcutta and Birbhoom, deduced from the sunrise, morning and afternoon observations, amounts to 4 degrees, which, if the mean height of the hills where crossed by the road, be called 1,135 feet, will be equal to a fall of one degree for every 288 feet.

In the dampness of its atmosphere, Calcutta contrasts very remarkably with these hills; the dew-point on the Hoogly averaging 51.3 degrees, and on these hills 38 degrees, the corresponding saturation-points being 0.559 and 0.380.

The difference between sunrise, forenoon and afternoon dew-points at Calcutta and on the hills, is 13.6 degrees at each observation; but the atmosphere at Calcutta is relatively drier in the afternoon than that of the hills; the difference between the Calcutta sunrise and afternoon saturation-point being 0.449, and that between the hill sunrise and afternoon, 0.190. The march of the dew-point is thus the same in both instances, but owing to the much higher temperature of Calcutta, and the greatly increased tension of the vapour there, the relative humidity varies greatly during the day.

In other words, the atmosphere of Calcutta is loaded with moisture in the early morning of this season, and is relatively dry in the afternoon: in the hills again, it is scarcely more humid at sunrise than at 3 p.m. That this dryness of the hills is partly due to elevation, appears from the disproportionately moister state of the atmosphere below the Dunwah pa.s.s.

II. _Abstract of the Meteorological observations taken in the Soane Valley (mean elevation 422 feet)._

The difference in mean temperature (partly owing to the sun's more northerly declination) amounts to 2.5 degrees of increase in the Soane valley, above that of the hills. The range of the thermometer from day to day was considerably greater on the hills (though fewer observations were there recorded): it amounted to 17.2 degrees on the hills, and only 12.8 degrees in the valley. The range from the maximum to the minimum of each day amounts to the same in both, above 20 degrees. The extreme variations in temperature too coincide within 1.4 degrees.

The hygrometric state of the atmosphere of the valley differs most decidedly from that of the hills. In the valley dew is constantly formed, which is owing to the amount of moisture in the air, for nocturnal radiation is more powerful on the hills. The sunrise and 9 p.m. observations in the valley, give a mean depression of the dew-point below the air of 12.3 degrees, and those at the upper level of 21.2 degrees, with no dew on the hills and a copious deposit in the valley. The corresponding state of the atmosphere as to saturation is 0.480 on the hills and 0.626 in the valley.

The vegetation of the Soane valley is exposed to a less extreme temperature than that of the hills; the difference between solar and nocturnal radiation amounting here only to 80.5 degrees, and on the hills to 96.5 degrees. There is no material difference in the power of the sun's rays at the upper and lower levels, as expressed by the blackbulb thermometer, the average rise of which above one placed in the shade, amounted to 48 degrees in both cases, and the maximum occurred about 11 a.m. The decrease of the power of the sun's rays in the afternoon is much the most rapid in the valley, coinciding with a greater reduction of the elasticity of vapour and of humidity in the atmosphere.

The photometer observations show a greater degree of sun's light on the hills than below, but there is not at either station a decided relation between the indications of this instrument and the black-bulb thermometer. From observations taken elsewhere, I am inclined to attribute the excess of solar light on the hills to their elevation; for at a far greater elevation I have met with much stronger solar light, in a very damp atmosphere, than I ever experienced in the drier plains of India. In a damp climate the greatest intensity may be expected in the forenoon, when the vapour is diffused near the earth's surface; in the afternoon the lower strata of atmosphere are drier, but the vapour is condensed into clouds aloft which more effectually obstruct the sun's rays. On the Birbhoom and Behar hills, where the amount of vapour is so small that the afternoon is but little drier than the forenoon, there is little difference between the solar light at each time. In the Soane valley again, where a great deal of humidity is removed from the earth's surface and suspended aloft, the obstruction of the sun's light is very marked.

DUNWAH TO SOANE RIVER, AND UP SOANE TO TURA, FEBRUARY 10-19TH.

Hour Sunrise 9 a.m. 3 p.m. 9 p.m.

TEMPERATURE Mean 57.6 74.0 77.6 64.5 Max. 62.0 81.0 87.5 68.7 Min. 53.5 63.5 71.0 60.0 Range 8.5 17.5 16.5 8.7 WET-BULB Mean 51.7 59.5 59.9 55.5 Max. Depression 8.5 18.5 26.0 12.5 Min. Depression 3.8 4.0 6.8 2.5

Elasticity of Vapour .352 .382 .357 .370

DEW-POINT Mean 46.1 48.5 46.4 47.5 Max. 53.6 56.7 60.0 55.6 Min. 40.6 38.0 36.0 41.0 Max. Depression 16.9 33.5 44.2 24.1 Min. Depression 7.0 6.8 11.0 4.4

Weight of Vapour in cubic feet 3.930 4.066 3.658 4.014

SATURATION Mean .680 .460 .352 .572 Max. .787 .818 .703 .860 Min. .566 .338 .237 .452

Number of observations 10 8 9 10

Extreme variations of Temperature 34.0 degrees Extreme variations of relative humidity .623 Extreme diff. Solar and Nocturnal Radiation 80.5 degrees

NOCTURNAL RADIATION

SUNRISE Exposed Th. On Earth On Gra.s.s Temperature 53.2 54.0 51.5 Mean Diff. from Air 4.5 3.7 6.2 Max. Diff. from Air 8.5 9.0 7.5 Number of Observations 9 9 8

NINE P.M.

Exposed Th. On Earth On Gra.s.s Temperature 59.9 60.7 56.4 Mean Diff. from Air 4.6 3.8 8.1 Max. Diff. from Air 11.5 10.5 13.5 Number of Observations 10 10 10

SOLAR RADIATION

MORNING Time Temp. Black Bulb Diff. Phot.

9 a.m. 70.0 125 55.0 10.300 11 a.m. 81.0 119 38.0 10.230 10.30 a.m. 71.5 126 54.5 10.300 10 a.m. 72.0 117 45.0 10.220 10 a.m. 80.0 122 42.0 ...

10.30 a.m. 78.0 128 50.0 ...

---------------------------------------------------- Mean 75.4 122.8 47.4 10.262

AFTERNOON Time Temp. Black Bulb Diff. Phot.

4 p.m. 76.5 90 13.5 ...

3 p.m. 80.0 105 25.0 10.210 3 p.m. 76.0 102 26.0 10.170 3 p.m. 87.5 126 38.5 ...

---------------------------------------------------- Mean 80.0 105.7 25.7 10.190

NOCTURNAL RADIATION FROM PLANTS

SUNRISE Air Temp. 59.5 55.0 Calotropis ... 49.5 Diff. ... 5.5 Argemone 57.0 47.0 Diff. 2.5 8.0

NINE P.M.

Temp. 67.5 67.0 64.3 Calotropis ... ... 58.5 Diff. ... ... 5.8 Argemone 53.0 56.0 57.0 Diff. 14.0 11.0 7.3

III. VALLEY OF SOANE RIVER, TURA TO SULKUN (MEAN ELEV. 517 FEET), FEBRUARY 20TH TO MARCH 3RD.

Hour Sunrise 9 a.m. 3 p.m. 9 p.m.

TEMPERATURE Mean 56.8 82.0 88.6 68.0 Max. 70.0 89.0 94.7 74.0 Min. 50.0 69.0 81.5 61.0 Range 20.0 20.0 43.2 13.0 WET-BULB Mean 52.5 61.2 62.4 56.8 Max. Depression 10.0 24.3 30.2 15.0 Min. Depression 1.5 12.0 14.5 6.0

Elasticity of Vapour .380 .385 .289 .369

DEW-POINT Mean 48.3 48.7 40.8 47.4 Max. 53.1 60.2 50.9 51.8 Min. 41.1 40.3 32.3 42.6 Max. Depression 17.3 45.2 57.2 27.1 Min. Depression 5.4 22.0 25.1 10.2

Weight of Vapour in cubic feet 4.240 4.097 2.975 3.933

SATURATION Mean .754 .342 .211 .511 Max. .831 .488 .598 .703 Min. .570 .226 .154 .415

Number of observations 12 11 11 11

Extreme variations of Temperature 44.7 degrees Extreme variations of relative humidity .677 Extreme diff. Solar and Nocturnal Radiation 100 degrees

NOCTURNAL RADIATION

SUNRISE Exposed Th. On Earth On Gra.s.s Temperature 51.7 52.4 48.8 Mean Diff. from Air 4.1 3.4 7.0 Max. Diff. from Air 8.0 7.0 11.5 Number of Observations 9 9 9

NINE P.M.

Exposed Th. On Earth On Gra.s.s Temperature 61.2 64.3 55.8 Mean Diff. from Air 6.8 4.6 11.8 Max. Diff. from Air 10.5 8.5 17.0 Number of Observations 10 9 9

SOLAR RADIATION

MORNING Time Temp. Black Bulb Diff. Phot.

11.30 a.m. 85.5 129 44.5 ...

10.30 a.m. 89.0 132 43.0 ...