al oscillation), it has no known fair weather standard. The point
of 30 inches is taken only as it is a mean. I have known it to commence
storming when the barometer was at 30.70, and not to fall before it
cleared off, below 30.30. And I have known it to be below 30 for several
days consecutively, with fair weather. In our climate there is no reliable
fair weather standard for the barometer. It falls below 30 without
storming; it rises far above, and storms without falling below. No
reliance can be placed upon its elevation, except by comparison; but of
that hereafter.

The general rule, nevertheless, is, that it falls more or less during
storms, whatever its height, and rises sooner or later, more or less,
after they clear off.

The difference between its highest and lowest points is called its range.
The greatest range observed, and recorded, is about 3 inches--from about
28 to 31--but this range is rare. The range, in the trade-wind region, is
comparatively small; in this country it is greater than in Europe; and,
generally, the range will be found greatest where the volume of
counter-trade, and magnetic intensity, and the corresponding amount of
precipitation, and extremes of heat and cold are greatest. One of the
greatest ranges during one storm, or two successive portions of a storm,
in this country, which I have seen recorded, occurred at Boston, in
February, 1842. It was as follows--counting the hours as 24, and from
midnight:

Feb. 15..10h..30.36.
" 16..13h..28.47 fall of 1.89 in 27 hours.
" 17..19h..30.39 rise of 1.92 in 30 hours.
" 18.. 2h..30.39 stationary 5 hours.
" 19.. 2h..29.46 fall of 0.93 in 24 hours.
" 20.. 2h..30.43 rise of 0.97 in 24 hours.
Amount of oscillation, 5.71 in 4 days, 11 hours.

These ranges were owing to the alternation of S. E. storms, and N. W.
winds.

Taking the first range as a basis, and allowing the height of the
atmosphere to be 1,100 feet for the first inch, we have nearly 2,000 feet
displaced during one day, if we look for the displacement near the earth,
or some 30 or 35 miles, if we soar aloft in the upper regions to look for
the _lateral overflow_ of Professor Dove, and about the same quantity
restored the next. This brings us to the inquiry, how was it done? It is
perfectly idle to talk about _difference_ of _temperature_ or _tension_ of
_vapor_, the _ascent_ of warm air, or _descent_ of cold in a case like
this; or to say that th