* On ice-built isles. l. 529. There are many reasons to believe from the accounts of travellers and navigators, that the islands of ice in the higher northern latitudes as well as the Glaciers on the Alps continue perpetually to increase in bulk. At certain times in the ice-mountains of Switzerland there happen cracks which have shewn the great thickness of the ice, as some of these cracks have measured three or four hundred ells deep. The great islands of ice in the northern seas near Hudson's bay have been ob∣served to have been immersed above one hundred fathoms beneath the surface of the sea, and to have risen a fifth or sixth part above the surface, and to have measured between three and four miles in circumference. Phil. Trans. No. 465. Sect. 2.
Dr. Lister endeavoured to shew that the ice of sea-water contains some salt and per∣haps less air than common ice, and that it is therefore much more difficult of solution; whence he accounts for the perpetual and great increase of these floating islands of ice. Philos. Trans. No. 169.
As by a famous experiment of Mr. Boyles it appears that ice evaporates very fast in severe frosty weather when the wind blows upon it; and as ice in a thawing state is known to contain six times more cold than water at the same degree of sensible coldness, it is easy to understand that winds blowing over islands and continents of ice perhaps much below nothing on Farenheit's scale, and coming from thence into our latitude must bring great degrees of cold along with them. If we add to this the quantity of cold pro∣duced by the evaporation of the water as well as by the solution of the ice, we cannot doubt but that the northern ice is the principle source of the coldness of our winters, and that it is brought hither by the regions of air blowing from the north, and which take an apparent easterly direction by their coming to a part of the surface of the earth which moves faster than the latitude they come from. Hence the increase of the ice in the polar regions by increasing the cold of our climate adds at the same time to the bulk of the Glaciers of Italy and Switzerland.
If the nations who inhabit this hemisphere of the globe, instead of destroying their sea-men and exhausting their wealth in unnecessary wars, could be induced to unite their labours to navigate these immense masses of ice into the more southern oceans, two great advantages would result to mankind, the tropic countries would be much cooled by their solution, and our winters in this latitude would be rendered much milder for perhaps a century or two, till the masses of ice became again enormous.
Mr. Bradley •••ribes the cold winds and wet weather which sometimes happen in May and June to the solution of ice-islands accidentally floating from the north. Treatise on Husbandry and Gardening, Vol. II. p. 437. And adds, that Mr. Barham about the year 1718, in his voyage from Jamaica to England in the beginning of June, met with ice-islands coming from the north, which were surrounded with so great a fog that the ship was in danger of striking upon them, and that one of them measured sixty miles in length.
We have lately experienced an instance of ice-islands brought from the Southern polar regions, on which the Guardian struck at the beginning of her passage from the Cape of Good Hope towards Botany Bay, on December 22, 1789. These islands were involved in mist, were about one hundred and fifty fathoms long, and about fifty fathoms above the surface of the water. A part from the top of one of them broke off and fell into the sea, causing an extraordinary commotion in the water and a thick smoke all round it.
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