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 certainty 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 aground. 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'sstraits, both sides of Baffin's-bay, Hudson'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-flood, 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 diminishing 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 perpetual supply from the northern parts.

[Phil. Trans. Abr. 1742.

SECTION VII.

Extraordinary Degree of Cold at Glasgow, in January 1780; with Experiments and Observations on the Comparative Temperature of the Hoar-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 annexed:

At six o'clock this morning Mr. W. carried the thermometer over to the Observatory Park, and there laid it down on the snow, when the mercury sunk to 13° below 0.

At this time he thought it unnecessary to stay abroad so long in the cold as to try the temperature of the air by hanging up the thermometers, especi

At 1 o'clock

2

2

+6°

14

+6

+4

+6

4

+3

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 4° at most in air at these two stations, Mr.W. was led into a suspicion that the snow might

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. the following observations, the interruption of the series from 24 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.

In

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 o'clock, when the thermometer pointed to -22°, the snow contigu ous to the ball was blown on for two minutes by a pair of hand-bellows, held with the pipe nearly horizontal, and half a foot above the surface of the snow. The bellows had been lying out on the snow to cool from the time Mr. W. first came over; and, in order to promote their cooling, they were now and then wrought in the open air. Care was also taken to stand to leeward of the thermometer, and to extend the bellows as far as possible from the body in the time of blowing. He was surprized to find however, notwithstanding all the precautions,

At Night.

9

10
11

Therm. on
the snow.

Therm. in the air.

12°

0°

14

11/2/2. Friday morn.

1

6

but the blast, though moderate, frequently drifted away the snow from the ball.

Exper. 2. At half past two o'clock, a bread-basket was filled with snow, taken up near the ground at + 14. The contents being relatively so warm, the basket was placed to leeward of the common station, and the thermometer laid on the surface of this snow. At the several hours in the morning, the thermometer on the basket pointed as annexed, viz.

At 3.

10°

3.

15

4.

<-161/

18

5

18

51

18

6.

18

4

At 5.

..-18

Exper. 8. At four in the morning, when the thermometer in the basket had got down to -16, a piece of this fir plank about a foot square was laid on the snow, on which was placed a small plate of tin which accidentally lay at hand. of the thermometers which had been hanging in the hir. At the several times it pointed as annexed.

On this was laid one

During the whole time not a cloud was perceivable, but there was a faint haze in the air when viewed towards the horizon. There was little or no tremor in the atmosphere, which made the stars shine with a full and steady light like that of the planets. Many of the town's people, who had thermometers hung out at their windows in different parts of the town, found them pointed several degrees below 0 at nine o'clock in the morning. On the afternoon of this day, January 14, the air became much warmer, and the barometer had now fallen 4-10ths. Next day a thaw came on, and continued for some time.

As the above experiment with the bellows favoured so little the opinion, that the difference of temperature was caused by evaporation, Mr.W. wished for another opportunity of making further experiments, and of inquiring into circumstances still more attentively. A good occasion offered on Satur. day, January 22. The frost, which before this time had again returned, became on this night very keen; and a good deal of the former snow yet remaining on the ground, the following observations and experiments were made at the observatory, viz. on Sunday morning January 23, at the several hours the two thermometers pointed as in the annexed table.

Exper. 4. This night instead of blowing on the snow, Mr. W. fanned it by means of a sheet of brown paper fitted to the end of a long slender stick. This apparatus was previously cooled by lying on the snow, and in fanning he took care to stand to leeward of the thermometer. The effect was, that the mercury rose nearly to the same degree given by the thermometer in air at the same time.

Exper. 5. At past one o'clock, when the thermometer on the snow pointed to + 3°, it was screened by two sheets of brown paper set up on their edges, and so inclined against each other as to stand. The paper had been previously cooled by lying on the At 24 the thermometer thus sheltered pointed to + 9o. This experiment was afterwards repeated with the same event.

snow.

Exper. 6. Mr.W. next went up to the leads of the east wing of the observatory. Here he hung a thermometer to the hook of a long pole, and raised it in the air about twenty-four feet from the ground, and at the same time inclined the pole over the ballustrade, so as to put the instrument fully to windward of the house. On suddenly lowering the pole, after half an hour, and examining the