At 9.30 a.m. the black-bulb thermometer rose in the sun to 130
degrees. 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 degrees), 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 vallies of the Soane and Ganges, and on the
elevated plateaus of Behar and of Mirzapore.* [See Appendix A.]

On the 2nd of February we proceeded to Tofe-Choney, the hills
increasing in height to nearly 1000 feet, and the country becoming
more picturesque. We passed some tanks covered with _Villarsia_, and
frequented by flocks of white egrets. The existence of artificial
tanks so near a lofty mountain, from whose sides innumerable
water-courses descend, indicates the great natural dryness of the
country during one season of the year. The hills and vallies were
richer than I expected, though far from luxuriant. A fine _Nauclea_