set down these, as they were found from a series of my own observations. The noonday heat, of what we call the summer air, is at 76; but the extraordinary heat of the summer air goes to 80, and upwards; I have seen it at 86; and, therefore, I have set this down in the scale as the hottest air of England; though there is an account in the Philosophical Transactions, that it has been observed at 88*. An hard frost in England is set down at 16; but I have myself seen the thermometer at 7°: and Thomas Hooker, esq. of Tunbridge, assured me, that in the late severe frost of 1776, at four o'clock one morning, he saw his own thermometer but half a degree above the cypher †. The subterranean temperature of the earth at moderate depths, in this latitude, is about 48 throughout the whole year. When the thermometer in the open air was at 85, another in my cellar (at Pluckley in Kent) the floor of which is about 10 feet below the surface of the earth, and goes into the rock with an arch

* I am informed that in this present summer, June 1780, it has been seen so high as 90 in the neighbourhood of London.

In the Gentleman's Magazine for March 1776, a diary is inserted from Chatham, where the thermometer is marked at 3 degrees below the cypher at Jan. 31.

arch of stone, was at 55; and in the late severe weather it was never below 36; but the mean betwixt these two is probably not the true one, because the extraordinary cold which sunk the thermometer, continued so much longer than the extraordinary heat that raised it.

I find, upon looking into my papers, that the temperature which I observed in the subterranean waters of the great cave in the Peak of Derbyshire was 48. The mean of all the middle heats above set down for the four seasons, is 46; whether the temper of the earth's body is quite so low as this, does not appear. At different depths the heat is various, and sometimes is found very high at very great depths*. These things being premised, we shall now be better able to judge of what we hear concerning the temperature of other climates.

In surveying the different parts of the world, we shall meet with a cool, or at least a moderate air, where we should expect the most violent heats; and shall likewise find great heats in the high northern latitudes, where we should expect a series of cold weather through the whole course of the year.

See Nollet, tom. iv. p. 68.

At

At the island of Jamaica, which is within the limits of the torrid zone, the heat is not nearly so disagreeable as in the south of Spain, Gibraltar, and Minorca: and at the north side of the island of Jamaica, when the wind blows off the continent, the air is cold, and a white frost is often seen upon the ground, but never any ice. Within twelve leagues of Carthagena, which is very near the line, the mountains are covered with snow. A regiment which had been abroad at Carthagena and Jamaica, was afterwards ordered into the Highlands of Scotland: and on one day in particular, as they were on their march in the Highlands, it was agreed by the officers and all the men, that they had never felt the heat so intolerable in the West Indies. Perhaps it ought to be considered, in accounting for this, that the heat is often very great in vallies, when it is much more moderate on the hills or level grounds, on account of the reflexion of the sun's rays, especially where there are rocks and cliffs of a light colour. But the extraordinary heat in our northern latitudes is chiefly to be accounted for from the long continuance of the sun above the horizon; so that what is wanting in the direction of his rays is

more

more than compensated by the duration of their influence. This is the reason why the summers are hot at Petersburgh in Russia, about 10 degrees north of London; where the corn is sown and grows up and ripens in a very short time, much sooner than in England. At Greenland, which is near 80 degrees north, the summer heat is excessive; insomuch that an experienced person, who was much versed in those parts, concluded it must be very great at the pole itself, on account of the long continuance of the sun above the horizon. In the Isle of Cherry, which is 75 degrees, the men who fish for the sea-calves are said to have felt so great an heat about mid-summer that the pitch melted and ran along the sides of their vessel. Many other extraordinary instances are to be met with, for which I cannot well account, unless we suppose that the sunshine, beside the duration of it, has some particular advantage in acting upon the denser air of the polar regions. On the other hand, the cold at Philadelphia in Pennsylvania, which place is 10 degrees nearer the sun than London, was observed to be 11 degrees below the cypher; and as the observation was not made in a sharp winter, it is supposed that

the

the cold may sometimes fall to more than 20 degrees below the cypher*. The heat of the summer at the same place arose to 96 or 97; which gives above 100 degrees for the annual range of the thermometer. At Barba

does the thermometer never rises above 86: yet at Valdagnio, within 60 miles of Venice, a learned observer assured me he saw the thermometer rise to 96 for ten days successively.

Muschenbroek informs us, that in July 1750, the heat at Leyden in Holland was 90: that the greatest heat of Senegal in Africa is from 104 to 110 degrees: and that in a voyage to Peru under the line, the thermometer was observed at 45 degrees.

All travellers who have frequented the European side of the Mediterranean sea, such as Gibraltar, Minorca, Venice, Sicily, &c. complain most of the hot wind that blows in those places, particularly in the night; the sensation of which is attended with a debility of the limbs, and a failing of the animal spirits, both of which are past expression. They give this wind the name of the siroco, because it comes to them from the south-east, and is supposed to arise from the lands of Africa

* Peter Kalm's Travels to North America, vol. i. p. 295.