NOCTURNAL RADIATION
SUNRISE
Exposed Th. On Earth On Grass
Temperature 59.5 56.0 54.7
Mean Diff. from Air 3.5 1.5 8.2
Max. Diff. from Air 3.5 1.5 8.5
Number of Observations 2 1 2
NINE P.M.
Exposed Th. On Earth On Grass
Temperature 71.5 62.5 61.0
Mean Diff. from Air 3.3 5.5 8.2
Max. Diff. from Air 7.0 5.5 11.0
Number of Observations 3 1 2
The rapid drying of the lower strata of the atmosphere during the day, as indicated by the great decrease in the tension of the vapour from 9 a.m. to 3 p.m., is the effect of the great violence of the north-west winds.
From the few days' observations taken on the Kymore hills, the temperature of their flat tops appeared 5 degrees higher than that of the Soane valley, which is 500 feet below their mean level. I can account for this anomaly only on the supposition that the thick bed of alluvium, freely exposed to the sun (not clothed with jungle), absorbs the sun's rays and parts with its heat slowly. This is indicated by the increase of temperature being due to the night and morning observations, which are 3.1 degrees and 8.5 degrees higher here than below, whilst the 9 a.m. and 3 p.m. temperatures are half a degree lower.
The variations of temperature too are all much less in amount, as are those of the state of the atmosphere as to moisture, though the climate is rather damper.
On the subject of terrestrial radiation the paucity of the observations precludes my dwelling. Between 9 p.m. and sunrise the following morning I found the earth to have lost but 6.5 degrees of heat, whereas a mean of nine observations at the same hours in the valley below indicated a loss of 12 degrees.
Though the mean temperature deduced from the few days I spent on this part of the Kymore is so much above that of the upper Soane valley, which it bounds, I do not suppose that the whole hilly range partakes of this increase. When the alluvium does not cover the rock, as at Rotas and many other places, especially along the southern and eastern ridges of the ghats, the nights are considerably cooler than on the banks of the Soane; and at Rotas itself, which rises almost perpendicularly from the river, and is exposed to no such radiation of heat from a heated soil as Shahgunj is, I found the temperature considerably below that of Akbarpore on the Soane, which however is much sheltered by an amphitheatre of rocks.
V. Mirzapore on the Ganges.
During the few days spent at Mirzapore, I was surprised to find the temperature of the day cooler by nearly 4 degrees than that of the hills above, or of the upper part of the Soane valley, while the nights on the other hand were decidedly warmer. The dew-point was even lower in proportion, 7.6 degrees, and the climate consequently drier. The following is an abstract of the observations taken at Mr. Hamilton's house on the banks of the Ganges (below).
It is remarkable that nocturnal radiation as registered at sunrise is much more powerful at Mirzapore than on the more exposed Kymore plateau; the depression of the thermometer freely exposed being 3 degrees greater, that laid on bare earth 6 degrees, and that on the grass 1.4 degrees greater, on the banks of the Ganges. During my passage down the Ganges the rise of the dew-point was very steady, the maximum occurring at the lowest point on the river, Bhaugulpore, which, as compared with Mirzapore, showed an increase of 8 degrees in temperature, and of 30.6 degrees in the rise of the dew-point. The saturation-point at Mirzakore was .331, and at the corresponding hours at Bhaugulpore .742.