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destruction in perpetual operation, as well as the
law of renovation—were they not invariably linked
as it were hand in hand, the surface of the earth
would become, in one extreme a desert, untenanted
by living things ; in the other, a self-destructive
crowd.
Returning to the phial, and therefore to all closed
vessels or buildings, we cannot fail to perceive, that
while all the agents of life, all the vivifying principles
are allowed the fullest scope for their operations, all
the destructive ones are in a greater or less degree
excluded : Nature is still at work : no particle of the
benefit results from human skill : we add no gases to
those around us in order to make the air more nourishing
: we subtract none to make it more pure. Atmospheric
humidity is one of the most important agents
in the vitality and luxuriant growth of Ferns; and
this is attained in closed cases, or under bell-glasses,
in such perfection, that the most moisture-loving of
all our species—Trichomanes speciosum, of which I
have before spoken, as growing only in the spray of
water-falls—not only lives but thrives. Mr. Ward
has this plant growing with a luxuriance and vigour
that can seldom be exceeded in a state of nature. In
the rapid transitions from heat to cold, so common in
our climate, and so particularly injurious to tender
vegetables, these cases offer a complete barrier : for
experiments prove beyond question that the atmosphere
within the glass retains its degree of temperature
very long after a change has taken place in the
air that surrounds it, and excess of cold, accompanied
by perfect stillness, is incomparably less injurious
than when coupled with rapid motion. Thus our
travellers in Polar regions speak of intense cold, as
indicated by the thermometer, having been scarcely
inconvenient to them if the atmosphere were perfectly
still; but if the wind rose, although the quicksilver
simultaneously fell, as was almost invariably the
case, the cold was most distressing. In Fngland,
if Fahrenheit’s thermometer be at 30", we walk about
or stand exposed to it without any sensation of pain,
but if we face it in travelling by railway at the rate of
thirty miles an hour, the cold becomes perfectly
intolerable. In fact, it has been abundantly proved
by experiment, that a much greater extreme of heat
or cold may be borne by plants, by animals, and even
by the human frame, if both the atmosphere and the
objects of experiments be in a state of perfect quiescence.
In closed cases we thus not only avoid rapid
changes of temperature, but the active motion in
extremes of temperature, which is the most injurious
property of such extremes. The deleterious effect of
boisterous winds on the fragile fronds of Ferns needs
no exemplification; it is so great, that if a specimen
of Cystopteris be moved from its protected habitat,
and placed where it may receive the full force of the
wind, that alone will, in a few weeks, work its utter
destruction: to such a plant how grateful must be
the motionless atmosphere thus provided!
The solution of the problem appears to me to be
fit