Some observations on the heat of wells and springs in the Island of Jamaica, and on the temperature of the earth below the surface in different climates / [John Hunter].

  • Hunter, John, -1809.
Date:
[1788]
Catalogue details

Licence: Public Domain Mark

Credit: Some observations on the heat of wells and springs in the Island of Jamaica, and on the temperature of the earth below the surface in different climates / [John Hunter]. Source: Wellcome Collection.

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    * 4 Dr. Hunter’s Obfervations on the Heat and the cold of winter, provided it contain no internal fourceof heat within itfelf. This conclufion is ftridtly agreeable to the experiments and obfervations hitherto made, in heating and cooling bodies, or in mixing portions of matter of the fame kind of di the rent temperatures *. Water, though in a large mafs, follows in fome degree the heat and cold of our fummer and winter, from the mobility of its parts occafioning a more fpeedy diffulion of heat. Air is quickly fufceptible of heat,and from the expanfions produced in it, and confequent motions in the whole mafs, the temperature is foon rendered uniform. The changes in the heat of the air are what we have meafured, and we are to be underftood to fpeak of them, when we talk of the temperature of fummer and of winter. It may be afked then, is the heat of the fun firfr communicated to the air, and thereby to the earth ? No, the air is fufceptible of a very fmall degree of heat from the rays of the fun paffing through it; for it is well known, they produce no heat in a tranfparent medium, and confequently, that the air is only fo far heated as it differs from a medium that is perfectly tranfparent. The heat produced by the rays of the fun bears a proportion to their number, their duration, and their falling more or lefs perpendicularly ; and it takes place at the points where they ftrike an opaque and non-refledting furface. The furface of the earth may there¬ fore be confidered as the place, from whence the heat proceeds, which is communicated to the air above, and the earth below. That this is really the cafe is evident from the fuperior degree of heat, produced by the adtion of the rays of the fun upon an opaque body, which will often be heated to 150° (Fahren¬ heit), while the temperature of the air is not above 90°f. It may feem, therefore, that to meafure the heat communicated •* Vid, De Luc Modifications de l'Atmofphere, Vol, I. p. 285. f Martine’s Eflays, p. 309. to