The temperature at 3 a.m. was 65°; at 3 p.m. 82° and at 10 p.m., 68°, from which there was no great variation during the whole time we spent at these elevations. The clouds were rare, and always light and high, except a little fleecy spot of vapour condensed close to the summit of Paras-nath. Though the nights were clear and starlight, no dew was deposited, owing to the great dryness of the air. On one occasion, this drought was so great during the passage of a hot wind, that at night I observed the wet-bulb thermometer to stand 20·5 degrees below the temperature of the air, which was 66° this indicated a dew-point of 11·5°, or 54·5° below the air, and a saturation-point of 0·146; there being only 0·102 grains of vapour per cubic foot of air, which latter was loaded with dust. The little moisture suspended in the atmosphere is often seen to be condensed in a thin belt of vapour, at a considerable distance above the dry surface of the earth, thus intercepting the radiation of heat from the latter to the clear sky above. Such strata may be observed, crossing the hills in ribbonlike masses, though not so clearly on this elevated region as on the plains bounding the lower course of the Soane, where the vapour is more dense, the hills more scattered, and the whole atmosphere more humid. During the ten days I spent amongst the hills I saw but one cloudy sunrise, whereas below, whether at Calcutta, or on the banks of the Soane, the sun always rose behind a dense fog-bank. At 9.30 a.m. the black-bulb thermometer rose in the sun to 130°. The morning observation before 10 or 11 a.m. always gives a higher result than at noon, though the sun’s declination is so considerably less, and in the hottest part of the day it is lower still (3.30 p.m. 109°), an effect no doubt due to the vapours raised by the sun, and which equally interfere with the photometer observations. The N.W. winds invariably rise at about 9 a.m. and blow with increasing strength till sunset; they are due to the rarefaction of the air over the heated ground, and being loaded with dust, the temperature of the atmosphere is hence raised by the heated particles. The increased temperature of the afternoon is therefore not so much due to the accumulation of caloric from the sun’s rays, as to the passage of a heated current of air derived from the much hotter regions to the westward. It would be interesting to know how far this N.W. diurnal tide extends; also the rate at which it gathers moisture in its progress over the damp regions of the Sunderbunds. Its excessive dryness in N.W. India approaches that of the African and Australian deserts; and I shall give an abstract of my own observations, both in the valleys of the Soane and Ganges, and on the elevated plateaus of Behar and of Mirzapore.[12] [12] See Appendix A.