Abbildungen der Seite
PDF
EPUB

small as fine hairs or threads, and pointed as sharp as needles, These icicles lodge in the cloaths; and if the faces or hands be un. covered, they presently raise blisters as white as a linen cloth, and as hard as horn. Yet if they immediately turn their backs to the weather, and can bear a hand out of the mitten, and with it rub the blistered part for a small time, they sometimes bring the skin to its former state: if not, they make the best of their way to a fire, and get warm water, with which they bathe it, and so dissipate the hu. mours raised by the frozen air ; otherwise the skin would be off in a short time, with much hot, serous, watery matter coming from under along with the skin; and this happens to some almost every time they go abroad for five or six months in the winter, so ex. tremely cold is the air when the wind blows any thing strong.

It is observed, that when it has been extreme hard frost by the thermometer, and little or no wind that day, the cold has not near so sensibly affected them, as when the thermometer has shewed much less freezing, having a brisk gale of northerly wind at the same time. This difference may perhaps be occasioned by those sharp-pointed icicles before mentioned striking more forcibly in a windy day than in calm weather, thereby penetrating the naked skin, or parts but thinly covered, and causing an acute sensation of pain or cold. And the same reason will probably hold good in other places.

It is not a little surprising to many, that such extreme cold should be felt in these parts of America, more than in places of the same latitude on the coast of Norway; but the difference seems to be occasioned by wind blowing constantly here, for seven months in the twelve, between the north-east and north-west, and passing over a large tract of land, and the exceedingly high mountains, &c. Whereas at Drontheim in Norway, as Captain M. observed some years ago in wintering there, the wind all the winter comes from the north worth-west, and crosses a great part of the ocean clear of those large bodies of ice found here perpetually. At this place they have constantly every year nine months frost and snow, and unsufferable cold from October till the beginning of May. In the long winter, as the air becomes less ponderous towards the polar parts, and nearer to an equilibrium, as it happens about one day in a week, they then have calms and light airs all round the compass, continuing sometimes twenty-four hours, and then back to its old place again, in the same manner as it happens every night in the West Indies, near some of the islands.

The snow that falls here is as fine as dust, but never any hail, except at the beginning and end of winter. Almost every full and change of the moon, very hard gales from the north. The constant trade-winds in these northern parts he thinks undoubtedly to proceed from the same principle which Dr. Halley conceives to be the cause of the trade-winds near the equator, and their variations. For that the cold dense air, by reason of its great gravity, conti. nually presses from the polar parts towards the equator, where the air is more rarefied, to preserve an equilibrium or balance of the atmosphere, is very evident from the wind in those frozen regions blowing from the north and north-west, from the beginning of October till May; for when the sun, at the beginning of June, has warmed those countries to the northward, then the south-east, east and variable winds, continue till October again; and doubtless the trade.winds and hard gales may be found in the southern polar parts to blow towards the equator, when the sun is in the northern signs, from the same principle.

The limit of these winds from the polar parts, towards the equa. tor, is seldom known to reach beyond the 30th degree of latitude ; and the nearer they approach to that limit, the shorter is the con. tinuance of those winds. In New England it blows from the north near four months in the winter; at Canada, about five months ; at the Dane's settlement in Davis's Straits, in the 63d degree of latitude, near seven months ; on the coast of Norway, in 64', not above five months and a half, because blowing over a great part of the ocean, as before-mentioned; for those northerly winds conti. nue a longer or shorter time, as the air is more or less rarefied, which may very probably be altered several degrees, by the na. ture of the soil, and the situation of the adjoining continents.

The vast bodies of ice met with in the passage from England to Hudson's-bay, are very surprising, not only as to quantity, but magnitude, and as unaccountable how they are formed of so great a bulk, some of them being immersed 100 fathom or more under the surface of the ocean; and a fifth or sixth part above, and three or four miles in circumference. Some hundreds of these are sometimes seen

voyage, all in sight at once, when the weather is clear. Some of them are frequently seen on the coasts and banks of Newfound.

in a

land and New England, though much diminished. When be calmed in Hudson’s-straits for three or four tides together, Capt, M. has taken a boat, and laid close to the side of one of them, sounded, and found 100 fathom water all round it. The tide flows here above four fathom; and he has observed, by marks on a body of ice, the tide to rise and fall that difference, which was a cer. tainty of its being aground. And in a harbour in the island of Resolution, where he continued four days, three of these isles of ice came agronnd. He sounded along by the side of one of them, quite round it, and found thirty-two fathom water, and the height above the surface but ten yards; another was twenty-eight fa. thom under, and the perpendicular height but nine yards above the water.

Captain Middleton accounts for the aggregation of such large bodies of ice in this manner: all along the coasts of Davis's. straits, both sides of Baffin's-bay, Hydson's-straits, Anticosh, or Labradore, the land is very high and bold, and 100 fathoms, or more, close to the shore. These shores have many inlets or fuirs, the cavities of which are filled up with ice and snow, by the almost perpetual winters there, and frozen to the ground, increasing for four, five, or seven years, till a kind of deluge or land-food, which commonly happens in that space of time throughout those parts, breaks them loose, and launches them into the straits or ocean, where they are driven about by the variable winds and currents in the months of June, July, and August, rather increasing than di. minishing in bulk, being surrounded, except in four or five points of the compass, with smaller ice for many hundred leagues, and land covered all the year with snow, the weather being extremely cold, for the most part, in those summer months. The smaller ice that almost fills the straits and bays, and covers many leagues out into the ocean along the coast, is from four to ten fathom thick, and chills the air to that degree, that there is a constant increase to the large isles by the sea's washing against them, and the perpetual wet fogs, like small rain, freezing as they settle on the ice; and their being so deeply immersed under water, and such a small part above, prevents the winds having much power to move them; for though it blows from the north-west quarter near nine months in twelve, and consequently those isles are driven towards a warmer climate, yet the progressive motion is so slow, that it must take up many years before they can get five or six hundred leagues to the

southward; probably some hundreds of years are required; for they cannot well dissolve before they come between the 50th and 40th degree of latitude, where the heat of the sun consuming the upper parts, they lighten and waste in time; yet there is a perpe. tual supply from the northern parts.

[Phil. Trans. Abr. 1742.

SECTION VIL.

Extraordinary Degree of Colil at Glasgow, in January 1780;

with Experiments and Observations on the Comparative Temperature of the llour-frost and Air near it, made at Macfarlane Observatory belonging to the College.

By Patrick Wilson, M,A. On Tuesday, January 11, 1780, there was a slight frost, and, on the evening of that day, a fall of snow to the depth of twelve inches. Next day the cold continued to increase, but so gradually, that at sun.set Fahrenheit's thermometer pointed only to 22°. About midnight, a very accurate thermometer, hung out at a high north window, soon after pointed to 6'. At this time the air was very still and serene, and the barometer stood at 30 inches.

Thursday morning, January 13, thermometer pointed as here andexed :

At six o'clock this morning Mr. W. At 1 o'clock +6° carried the thermometer over to the Ob. 1

+6 servatory Park, and there laid it down 21 on the snow, when the mercury sunk

2

+6 to 13° below 0.

4

+3 At this time he thought it unneces. 44

+2 sary to stay abroad so long in the cold

5

+2 as to try the temperature of the air by 5.1

to hanging up the thermometers, especi ally as he imagined that this had been done more readily, and as truly, by taking the degree from the surface of the snow which had been exposed to the open air during the night: but reflecting afterwards on the snow at the observatory being so much below 0, the greatest cold of the air at the college, and having on other occasions found a difference of only 4o at most in air at these two stations, Mr.W. was led into a suspicion that the snow might

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

+4

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

.

[ocr errors]

perhaps have been so far cooled down by an evaporation at the surface. With a view to this opinion, he projected the experiment with the bellows described below, by which he was not without expectations of producing a still more remarkable fall of the ther. mometer when lying on the snow. All the afternoon the cold was very intense, and at seven o'clock at night the thermometer at the high north window pointed to 0. At eight Mr. W. repaired to the observatory, and made choice of a station at a sufficient distance from the house, and to the windward, as a light air was felt com. ing from the east. Here he laid down two thermometers on the snow with their balls half immersed, and hung up other two freely exposed to the air at two feet and a half above the surface. In the following observations, the interruption of the series from 21 to 6 o'clock, was owing to an accident having befallen one of the thermometers while the other was employed in the trials, of which an account is subjoined.

Thursday evening, January 13, the two thermometers pointed at the degrees below 0, as in the following table, at the times annexed. Exper. 1. At half past one

Therm, in o'clock, when the thermometer At Night. pointed to -22°, the snow contigu. 8.

-12°

0° ous to the ball was blown on for two 9

14

2 minutes by a pair of hand-bellows, 10

14 held with the pipe nearly horizon. 11

17

6 tal, and half a foot above the surface 114. 18

6 of the snow. The bellows had been Friday morn. lying out on the snow to cool from

} .
20

- 8 the time Mr.W. first came over ; 1

23

7 and, in order to promote their 1. 22

8 cooling, they were now and then 2

22

9 wrought in the open air. Care was 21 / .

8 also taken to stand to leeward of the 3

9 thermometer, and to extend the 31

10 Bellows as far as possible from the 4

12 body in the time of blowing. He 41

12 was surprized to find however, 5

12 notwithstanding all the precautions, 51

12

Therm. on
the snow.

the air.

[ocr errors]
[ocr errors]

.

[ocr errors]
[ocr errors]

.

.

.

[ocr errors]
[ocr errors]

.

.

[ocr errors]

21

[ocr errors]
[ocr errors]
[ocr errors][merged small][merged small][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][merged small]
« ZurückWeiter »