108 The Weather. 



equal temperature, or " Isotherms," as they are called (10-09, 

 equal; Oepfios, hot), are drawn round the globe, giving equal 

 weight to every place. It is then found that the temperature 

 of the air on the western coasts of Europe is higher, especially 

 as compared with the eastern coasts of Asia and America, than 

 the ordinary temperature for the latitude. The same excess is 

 also observed on western, as compared with eastern coasts in 

 every part of the world, but the annual range of temperature 

 is less. Thus, from Gibraltar to Norway the range varies 

 between 15° and 35° (F.). From Florida to Labrador, on the 

 opposite coast of America, the annual range of temperature 

 varies between 30° and 50° (F.). At Pekin, on the eastern 

 coast of Asia, in the latitude of New York, the range of tem- 

 perature is 60° (F.), but near Vancouver's Island, in higher 

 latitude, on the western coast of North America, it is not so 

 great by half, or less than 30° (F.). 



In this general feature of the weather, the predominating 

 winds play an important part, as will hereafter be explained. 

 Not only do they elevate the temperature, but, bringing with 

 them clouds, the land under their influence neither loses nor 

 acquires its heat so rapidly as in countries less affected by their 

 action. 



On the borders of the Great Sahara, at sunrise in December, 

 it is no uncommon occurrence for ice to be found upon the 

 shallow pools. In our own climate hoar-frost is occasionally 

 produced in June. On the parched plains of Bengal ice is 

 artificially prepared by exposing water at night in shallow 

 vessels to the sky. Thus Jacob, in Scripture, speaks to 

 Laban : — " In the day the drought consumed me, and the frost 

 by night." The history of Gideon's fleece receives support 

 from the copious dew found by travellers on the sides of lakes, 

 rivers, and the sea in Palestine and Arabia. These facts are 

 very illustrative of the rapid radiation from the earth under 

 calm and cloudless skies. Dew and hoar-frost are thus pro- 

 duced. 



On undulating ground and verdant slopes the cold air from 

 the inclines collects on calm nights in hollow basins at their 

 feet. The line of contact with the warmer and moister air 

 above is marked by a thin horizontal sheet of fog, producing 

 from above the winding appearance of a river, or the wide and 

 waste appearance of a lake. These radiation fogs, as they are 

 called, are raised and dissipated at sunrise by the heat of the 

 sun, whose rays in their turn produce by day an exactly oppo- 

 site effect. 



Air at the surface of the earth exposed to an unclouded 

 sun becomes charged with heat and vapour. It is rendered 

 buoyant, and rapidly ascends to a height where its excess of 



