1319.] P ro f' Leslie on Heat and Climate. 21 



antiquity abundantly testify, that through the whole of Europe, 

 and in some parts of Asia, the winters were formerly much 

 severer than in the present times. I might cite many remarkable 

 passages to this purpose, were I not apprehensive of extending 

 this paper to an unusual length. Some late writers have indeed 

 admitted the fact, but have ascribed it to the clearing of the 

 forests, the draining of the marshes, and the general amelioration 

 of the globe. But these causes evidently will not apply to Italy. 

 That delightful country is divided on all sides from the rest of 

 the world by the sea and by ridges of lofty mountains. Its 

 ancient condition was flourishing and vigorous ; its modern is 

 sunk into insignificance and abject superstition. When it 

 formed the seat of temporal empire, the wealth which flowed in 

 from the provinces was mostly spent by the opulent Romans on 

 the cultivation and improvement of the soil, and on the decora- 

 tion of rural scenery, of which they were passionately fond. 

 Besides, we shall presently be convinced that the clearing of a 

 country has not the smallest effect in promoting the general 

 warmth of the climate. The true tendency of such a change on 

 the surface is to diminish somewhat the inequalities of the sea- 

 sons ; and this fact may serve to reconcile the apparently con- 

 tradictory accounts transmitted from the ancients. The summers 

 were formerly warmer upon the whole than at present, though the 

 winters were much colder. Vineyards were cultivated in Britain 

 by the Roman colonies. It is sufficient for the perfection of 

 plants that they enjoy the due heat during the season of growth. 

 In Virginia the winters are intensely cold ; yet that country 

 yields spontaneously many of the fruits of a tropical climate. 

 For the same reason some exotic plants are raised in open air 

 near St. Petersburg which require the assistance of artificial 

 heat in the vicinity of London.* 



If the earth had not been clothed with an atmosphere, an 

 immense diversity of climate would have obtained. The quan- 

 tities of light received from the sun during the revolution of a 

 year at the Equator, at London, and at the Pole, may be calcu- 

 lated to be as the numbers 31, 23, and 12 ; and consequently if 

 the action of the sun's rays were confined to the surface, the 

 parallel of London must have been colder than the Equator by 

 516°, and the Polar regions by 1,226°. In the long succession 

 of ages, however, the portions of heat received in different lati- 

 tudes would gradually penetrate toward the centre, and mingling 

 in their progression, would, in some measure, temper the system. 

 This consideration might somewhat diminish the above quanti- 

 ties, yet the diversity of climate would still be prodigiously 



* If experiments on the temperature of springs or wells were carefully made 

 and recorded, it would gratify our latest posterity, who might thence incontro- 

 vertibly decide whether the heat of the globe be progressive. The common regis, 

 ters of the weather are of little use in a philosophical point of view. The height 

 of ihe thermometer, being marked only at certain hours of the day, can never give 

 the true average heat of the climate. 



