Abbildungen der Seite
PDF
EPUB

104

SPECIAL STATES AND ADJUSTMENTS.

density is only partial, and is restrained by the aggregate amount equalizing it, so that it has no power or tendency to rush down upon the lighter air of the warmer regions, for the balance is held equally, and the impetuous and chilling power is kept at bay, and preserved in general quiescence within its own territory. By this arrangement the temperature is greatly limited, for, as the winds are caused by barometric pressure, if the polar region had a higher barometer, there would be a perpetual, or more frequent north wind.

Another extremely interesting illustration may be seen in the table of Mauritius, which gives a mean barometer of 30:11 inches to its warmer and sunny climate. It is an anomaly to have the greater weight of atmosphere amid the lighter air of the tropics. But here, again, we are called upon to admire and adore the Almighty Being, whose infinite wisdom has arranged every department of nature in a manner so wonderfully adapted to every required exigency as to surpass all the intellects of men fully to discern.

If from the testimony of the barometer we were called upon to assume a warmer air above in the polar circle, we are here constrained, by parity of reason, to assume a colder portion of air above in this particular region. For it is a particular region which envelopes or encircles the margin of the tropics, and encloses them as with a lofty wall of air. On the verge of either tropics there is an atmospheric belt or zone of high pressure – a hot region, a dry region of peculiar

THE HIGH PRESSURE OF THE ULTRA TROPIC ZONE. 105

character-extending 8° or 10° of latitude, and of equal extent with the zodiac, and perhaps it might be called the zodiacal region, as being parallel to it.

Now this amazing belt or zone of high pressure (mean barometer 30·11) stands as a lofty mountain ridge of air between the tropics and the temperate climates. And what is the extraordinary result of this ordination ? Why, as streams flow down equally on either side the mountains, so from this mighty zone of air of high pressure, currents of wind fly off or are impelled from either side. From hence proceeds the cool refreshing trade winds of the tropics, while from the other side, the grateful, soft, and balmy breezes blow mostly into the cooler regions, as the S.W. winds of our own climate. Hence a double benefit arises—two blessings at one time, of north and south winds, hot and cold, by one act, and each where needed. How kind and gracious! How this high pressure is permanently maintained does not appear; we must rest content at present with the fact, and with a grateful estimation of its immense effects and its world-wide benefits.

There are, likewise, some states of barometer in our own climate which have not been satisfactorily accounted for, as the extremely low barometer occasionally in the winter months. Are we to suppose in these cases that a larger volume of warm air and vapour prevails, or is present in the atmosphere then than in the summer? For warm air, charged with vapour, is specifically lighter than cold air, and, consequently we

assume the barometer to be lower with such.

How comes,

106

OUR LOWEST BAROMETER-WAY IN WINTER.

w

But our

then, our lowest barometer to be in the winter months ?
Are we disposed to admit the same principle we have
assumed to prevail in the polar regions-viz., that a
larger mass or volume of warmer air exists above ?
Such appears a difficult assumption, and hard to
reconcile with our preconceived opinions.
low winter barometer, the polar regions, and the ultra
tropical zone of high pressure, all are referrible to one
and the same cause--viz., volumes or beds of air of
different temperatures at various altitudes.

It is true, some may be disposed to refer the whole to
aërial waves, or tides of high and low columns of air,
like those of the waters of the ocean. No one, how-
ever, knows, or has any means of knowing, anything
about the lofty summits of the atmosphere. We can
only reason upon what we know, and from what we
see, and we have abundant evidence of
currents of air at different altitudes, and beds of ai
possessing varying temperatures, and these

seen adequate to effect the changes we experience and observe in the instruments.

In connection with this subject, I cannot do bette than add a few remarks from the observations of Lieut Foster, at Port Bowen, from Captain Parry’s Second Voyage. Lieut. Foster was a first-rate observer, and was especially furnished with the best instruments. He was indefatigable, and received the gold Copley Medal of the Royal Society of London, bearing the inscription of “Optissima,” as an estimation of the value of his labours and observations, and was, moreover, promoted

opposite

CAPTAIN FOSTER's “OPTISSIMA”

OPTISSIMA" OBSERVATIONS. 107

[ocr errors]
[ocr errors]
[ocr errors]

P. M.

Commander to the “Chanticleer,” on a voyage of research :

Particular attention was paid to the barometer during this winter, to which much encouragement was given by the excellence of the instruments furnished to us under the superintendence of Mr. Daniell. The most rigid attention during several months discovered a diurnal or horary occillation amounting only to ten thousand parts of an inch. The times of maximum and minimum appeared decidedly to lean to four and ten, and to follow a law directly the reverse of that found to obtain in temperate climates; the column being highest at four and lowest at ten o'clock both A. M. and

The barometer did not appear before-hand to indicate the changes of the weather with any degree of certainty. Alterations in the column more frequently

accompany than precede the visible changes of weather ds of ai in these regions.

“During this, as in all the preceding winters, we failed nce and to obtain any hygrometrical expression for the state of

the atmosphere, though we were furnished with the o bette most excellent hygrometers of Professor Daniell. Below f Lieut a temperature of 6° above zero we failed to obtain any Secono deposit of vapour. That the atmosphere was extremely

se

seen

dry, was evident, for a worn whale line, sixteen hundred ts. He and fourteen feet in length, being stretched quite tight sedal of between the Hecla' and the shore, for the purpose of cription marking the road in dark weather or snow drifts, relaxed

of his so much during the cold weather, that forty-nine Smotec feet were hauled in from time to time to keep it

ver, anc

108

ABSENCE OF VAPOUR, YET EVAPORATION.

in its place upon the snow pillars upon which it was supported

“Although we could not detect the presence of any moisture in the air, yet some evaporation was going on, because a brass instrument entirely sheltered from the wind, may one day be seen covered with numberless minute snow crystals adhering firmly to the metal, and the next perfectly clean and bright without any possible assistance from wind or artificial heat."

There was no want of well defined clouds this winter of the kind called cirro stratus. The depth of snow which fell during the winter was only about four inches. The crystals were extremely minute. The weight of a cubic foot of this fine snow dug out of a drift was thirty pounds.

The ice formed upon the canals by which the ships had entered, increased in the following ratio :

In November it was 30 inches in thickness.
In December

38
In January

45 In February

55 In March

73 In April

82 In May

86

[ocr errors]
[ocr errors]

Although the effect of the season in changing the colour is well known, I will merely mention that of Canis Lagopus. One or two foxes were killed and four were caught in traps during the winter. The colour of one of these animals, which lived for some time on board the “Fury," and became tolerably tame,

« ZurückWeiter »