on the Marine Barometer. 
261 
The cause of the sensibility of the mercury to winds blow- 
ing from the sea and from off the land, may perhaps admit of 
more than one explanation ; but the following seems to me to 
be direct, and tolerably satisfactory. The lower air, when 
brought in by a wind from the sea, meets with resistance in 
passing over the land ; and to overcome this resistance, it is 
obliged to rise, and will make itself room by forcing the su- 
perincumbent air upwards. The first body of air, that thus 
comes in from the sea, being itself obstructed in its velocity, 
will obstruct the second, which will therefore rise over the 
first in like manner, to overcome the obstruction ; and as the 
course of the second body of air will be more direct towards 
the top of the highest part of the land it has to surmount, 
than the first was, so the first part of the second body will 
arrive at the top, before the latter part of the first body has 
reached it ; and this latter part will not be able to pass over 
the top, being kept down by the second body and the succes- 
sive stream of air, whose velocity is superior to it. In this 
manner, an eddy, or body of compressed, and comparatively 
inactive air will be formed, which, at first, will occupy all the 
space below a line drawn from the shore to the top of the 
highest land ; but, almost immediately, the succeeding bodies 
of air, at a distance from the shore, will feel the effect of the 
obstruction ; and being impelled by those that follow them, 
will begin to rise, taking their course for the top of the highest 
land, before they come to the shore ; by which means, the 
stratum of lower air will be deeper between the top of 
the land and the shore, and to some distance out from it, than 
it is either upon the mountains or in the open sea. If this is 
admitted to be a necessary consequence of a wind blowing 
