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as to make them somewhat difficult to follow and explain. 
This is more particularly the case with those alterations that 
are consequent on the annual revolution of the earth ; whilst 
its daily rotation on its axis, presenting portions of its surface 
successively to the action of the solar heat, permits the 
influence of that heat on the water of the earth to be more 
readily followed and examined. The hourly disturbances of 
the atmosphere, by solar heat, are therefore first examined ; 
and it is shown that a little before sunrise evaporation of 
water becomes more energetic, sending vapour into the air 
which increases the total weight of the atmosphere, and makes 
the barometer rise without producing other disturbances until, 
say, ten o’clock. After ten, more vapour is furnished by 
evaporation, yet atmospheric pressure is not increased, but, 
on the contrary, diminishes ! This diminution is maintained 
to be caused by ascent of vapour to a sufficient height to be 
condensed into particles of water by the cold of the gases ; 
and the condensation liberates heat that was contained in the 
vapour, which heat warms and expands the gases. This 
expansion, forcing some of the air to go into adjoining parts, 
renders the locality lighter, — as is palpably shown in many 
places by a sea breeze, and the falling of the barometer. 
When the mid-day condensation of vapour is moderate it 
produces but a slight disturbance, and generally terminates 
about four o’clock in the afternoon, leaving clouds floating in 
the air. These clouds then begin to dissolve by evaporation 
into transparent vapour, taking heat from the gases in the 
locality, which makes them heavier, and they sink to the 
surface of the earth where they are generally known by the 
name of “ land winds.” The greater w'eight of this cooled 
local air makes the barometer rise until about ten o’clock, p.ni. 
But after this hour the absence of the sun permits the earth to 
cool, and to convert some of the vapour into dew ; — and the 
barometer falls in proportion to the extent to which vapour is 
thus liquified. Mr. Hopkins, therefore, maintains that total 
