Himalayan Journals, vol 2 by J. D. Hooker (android pdf ebook reader TXT) 📕

Max. .680 .450 .320 .590

Min. .330 .260 .190 .140

Number of observations 7 7 7 10

Extreme variations of Temperature 35.4 degrees

Extreme variations of relative humidity .540

Extreme diff. Solar and Nocturnal Radiation 96.5 degrees

*Taken during a violent N.W. dustt-storm.

SOLAR RADIATION

MORNING

Hour Th. Black Bulb Diff. Phot.

9.30 a.m. 77.0 130 53.0 ...

10 a.m. 69.5 124 54.5 10.320

10 a.m. 77.0 137 60.0 ...

9 a.m. 63.5 94 30.5 10.230

9 a.m. 61.2 106 44.8 ...

9 a.m. 67.0 114 47.0 10.350

Mean 69.2 117.5 48.1 10.300

AFTERNOON

Hour Th. Black Bulb Diff. Phot.

3.30 p.m. 81.7 109 27.3 ...

3 p.m. 80.5 120 39.5 10.320

3 p.m. 81.5 127 45.5 10.330

3.30 p.m. 72.7 105 32.3 10.230

3 p.m. 72.5 110 37.5 10.390

Mean 77.8 114.2 36.4 10.318

NOCTURNAL RADIATION

SUNRISE

Temperature 51.1 48.3 46.6

Mean Diff. from Air 4.0 2.5 6.2

Max. Diff. from Air 9.0 3.7 9.0

Number of Observations 6 3 5

NINE P.M.

Temperature 56.4 53.8 54.4

Mean Diff. from Air 5.3 4.9 7.2

Max. Diff. from Air 7.5 5.5 10.0

Number of Observations 7 6 7

On one occasion, and that at night, the dew-point was as low as 11.5

degrees, with a temperature of 66 degrees, a depression rarely

equalled at so low a temperature: this phenomenon was transient, and caused by the passage of a current of air loaded with dust, whose

particles possibly absorbed the atmospheric humidity. From a

comparison of the night and morning observations of thermometers laid on grass, the earth, and freely exposed, it appears that the grass

parts with its heat much more rapidly than the earth, but that still the effect of radiation is slight, lowering its temperature but 2

degrees below that of the freely exposed thermometer.

As compared with the climate of Calcutta, these hills present a

remarkable contrast, considering their proximity in position and

moderate elevation.

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 pass.

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.