190 HEAT OF THE WATERS. 



north as 50° N. L., and in Asia it seems to be 

 confined within a more southern limit. It is true 

 that, in the regions north of 50° N. L., there are 

 plenty of hot days in their summer, but that 

 summer is too short, and in September, just at 

 the time when the grape begins to ripen, there is 

 no longer sufficient heat in the day. And the 

 vine-plant cannot bear the cold of the continental 

 winter. The heat of the torrid zone is equally 

 little suited to the growth of the vine. Generally 

 therefore it does not grow within the tropics. 



Any great abundance of water in a country, 

 numerous lakes, swamps, marsh-lands, and exten- 

 sive forests, in which the moisture of the air is 

 retained, and gradually dissipated into the atmo- 

 sphere by evaporation, exert, to some extent, the 

 same influence as the sea, in mitigating the cold 

 of winter, and in lowering in turn the heat of 

 summer. By the draining of swamps, and the 

 cutting down of forests, the escape of the water is 

 hastened, and at the same time a greater extent of 

 the ground is exposed to the immediate influence 

 of the sun ; the limits of temperature of the day, 

 as well as of the year, are removed farther and 

 farther apart; the summers become warmer, the 

 winters colder, without any accompanying altera- 

 tion in the whole effect of the sun. This explains 

 the gradual change in the climate of countries, 

 which have been inhabited for thousands of years. 

 Thus there can be no doubt that Egypt, if it were 



