le atmospheric pressure. As the dry air and the aqueous vapor
mixed with it, press in common on the barometer, so that the up-borne
column of mercury consists of two parts, one borne by the dry air,
the other by the aqueous vapor, we may well understand that as with
increasing temperature the air expands, and by reason of its
augmented volume rises higher, and _its upper portion overflows
laterally_," etc.

And in another place he says:

"From the magnitude of the variations in the northern hemisphere, and
the extent of the region over which it prevails, we must infer that
_at the time of diminished pressure a lateral overflow probably takes
place_," etc.

Doubtless, the mean pressure of the atmosphere, in summer, in the northern
hemisphere, is less than in winter, in some localities, and greater in
others, and it differs in different countries of equal temperature. And
this is all very intelligible. The mean of the pressure for the month is
made up by _averaging_ all the _elevations_ and _depressions_. During a
month, showing a very low mean, the barometer may, at times, attain its
_highest altitude_, if the depressions below the mean are great or more
frequent. The barometer is depressed during storms, and ranges high during
_set fair_ weather. Ordinarily, therefore, the more stormy the season the
more diminished the mean pressure; and it is a mistake to look to an
overflow to account for the fact. The changes in the location of the
atmospheric machinery, and consequent change in the amount and severity of
falling weather, and the periodic frequency and character of storms, and
consequent _periodic_ depressions and elevations of the barometer,
explain the annual mean variations, as they do the other phenomena. But it
is perfectly consistent with the calorific theory to attempt to account
for these differences by another of those ever-necessary modifications,
viz.: the different tension and elasticity of aqueous vapor in different
countries of equal temperature; and then to _suppose_ an expansion of the
whole body of the atmosphere and a lateral overflow from the place where
the air is expanded, on to some other, where it is not; and thus _suppose_
all necessary currents in the upper regions, setting hither and yon, by
the force of gravity alone. And apparently he who is best at supposition
becomes the most distinguished meteorologist. Perhaps I have already said
all