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thermometer at Ensleigh, during the three years for which the 
joint registers run parallel, is exactly one degree and a half in 
excess of what it is at the Institution, owing chiefly, as shown 
above, to the greater depression of the night temperature at the 
former place. 
The mean temperature of the dew-point also, like that of the 
air, except in a very few instances, is lower at Ensleigh than at 
the Institution, the mean difference for the whole period being 
nearly two degrees. But the mean depression of the dew-point below 
the temperature of the air, which is of more importance as more 
directly connected with the humidity of the atmosphere, is less 
than at the Institution, showing that, notwithstanding a lower 
dew-point, the humidity more nearly approaches the saturation 
point. 
This, perhaps, is not what some persons would expect, that 
there should seem to be more vapour in the air upon the hills, 
than in the valleys by the river-side. But it is the relative, not 
the absolute, humidity of the air which is here spoken of, the 
difference between which has been already explained. And in 
reference to the circumstance itself it may be remarked that though 
the valleys during the night and early part of the day, in particular 
_ States of weather, are often full of mist—the mist reaching up the 
hills to a certain height while the tops of the hills are clear—these 
- mists, as the day advances and the sun acquires more power, are 
_ gradually taken up by the atmosphere, and pass into the form of 
_ invisible vapour, which keeps continually ascending till it reaches 
the vapour-plane or cloud-region. The quantity of moisture in 
the air, therefore, will increase in proportion to the altitude, while 
the temperature of the air will Jessen in proportion to the altitude ; 
_and hence arises the circumstance of the difference between the 
temperature of the dew-point and the temperature of the air being 
less at Ensleigh than at the Institution. Such is, moreover, in 
accordance with what has been observed by meteorologists who 
have made balloon ascents. Mr. Welsh in each of four such 
