62 Proceedings of the Asiatic Society. [Marcn, 
the daytime and decrease towards early morning, forming a curve 
of single variation. From September to May the curve is more 
complicated. It presents a rise for an hour or two after sunrise ; then 
in most months a rapid and deep depression to a minimum about 
3 or 4 Pp. M., after which the rise is very rapid to 7 or 8 Pp. M. and 
thereafter (in the hot months) gradual to midnight. From this 
hour it falls again to sunrise. In December and January, the 
absolute minimum is at sunrise, in the other months in the afternoon, 
and itis deepest in March, (the driest month). The absolute maxi- 
mum is in the evening or at midnight from October to March, and in 
the morning in April, May and June. The curve generally for all 
these months may be described as one conforming to that of tem- 
perature, but with a deep notch cut out of it during the warmer 
hours of the day, thus producing two crests, of which the earlier is 
the higher in the hottest months the later in the remainder. This 
form of curve is well known as characterizing a continental climate, 
and something similar, but much less in the relative and absolute 
magnitude of the afternoon depression, obtains at certain stations 
in the interior of Kurope during the summer months. ‘The curves 
of saturated vapour pressure are given for comparison, and the 
ratios of the two are shewn by the humidity curves which are almost 
an exact inversion of those of temperature. The temperature 
curves are of the same general form throughout; differing chiefly 
in the absolute magnitudes of their ordinates which are greatest 
in March, the driest, least in July and August the dampest months, 
The next set of curves that I have to exhibit are the diurnal 
barometric curves for Simla, deduced from Major Boileau’s hourly 
observations for 3 years. They are as regular and shew nearly 
as great a range of tidal pressure as those of Calcutta, but with 
this marked difference, that in all months except July and August 
the morning (4 A. M.) is the absolute minimum of the day. This 
peculiarity of the barometric curve has been noticed by Planta- 
mour in the case of the Great Saint Bernard, and is stated to be 
characteristic of mountain stations situated on ridges, as distin- 
guished from stations on plateaux and plains. The explanation 
given, I believe, by him is that the lower strata of the atmosphere 
3 being heated, lift a larger proportion of the upper atmosphere above 
