654 SCIENTIFIC RECREATIONS. 



The line of the snow limit, as a rule, gets lower as we journey from 

 the equator to the poles. Exception will be found in the Himalaya, where 

 the snow line is higher on the northern side, in consequence of the existence 

 of the Thibetan tableland, which causes a higher temperature than that 

 existing upon the abrupt southern slope. Countries, therefore, though in 

 the same latitude, may have different climates according to the elevation of 

 the land. 



The proximity to the sea is another reason for climatic difference. 

 Water takes some time to become warm, but when it has once become so it 

 will not readily part with its heat. The Gulf Stream, with its warm current 

 beating along our shores, gives us a high temperature and a moist climate 

 a very different condition to Newfoundland or Nova Scotia, which are in 

 much the same latitude as England and Ireland. By the sea the climate is 

 more uniform, and the extremes of heat and cold are not so distant. We 

 send invalids to the seaside to save them the effects of such violent changes. 

 Winters are milder and summers cooler by the sea. 



We can readily understand how such circumstances affect the vegetation, 

 and places which in winter may enjoy a mild and genial climate (compara- 

 tively speaking), may have a cold summer. Ferns may flourish in winter 

 out of doors, but wheat will not ripen in the autumn owing to the want of 

 heat. 



The winds also, and the soil and aspect of a region, all have a share in 

 determining its climate. Trees bring rain by evaporation, and a wooded 

 country is a blessing to its inhabitants, defending their habitations from 

 wind and avalanches in mountainous districts. But the climatic conditions 

 are altering. The ground is being more and more cleared ; the soil is more 

 cultivated, and moisture is being more eliminated from it. Therefore the 

 air becomes warmer by the radiation of the ground, and 'clouds are formed 

 which keep the warm layers down nearer the earth. Mountains, as we have 

 seen, affect the rain-fall in districts ; and in Scandinavia in Norway chiefly 

 the average rain-fall is very high. The sheltering effects of mountains 

 from east or northerly winds also alter the climate, while clay or gravel soils 

 are cold or warm inasmuch as they absorb, or evaporate, moisture. Some 

 surfaces being different from others give out more heat. 



In some mountainous districts we shall find every variety of climate 

 from the sea-level tropical heat to the rigours of the pole. The greatest 

 average temperature is north of the equator in Africa ; the lowest in the 

 north, to the west of Greenland. Masses of land act in a different manner 

 to the oceans, and the former become heated and cooled with equal rapidity, 

 while the sea, as already mentioned, is slow to lose its heat. Our land 

 enjoys a mild and equable climate as a rule, because it is surrounded by 

 water, and the Gulf Stream warms it. The European climate, taken alto- 

 gether, may be considered the best on the globe. 



We will now pass on to a few observations concerning the weather, and 

 the means of determining it beforehand. 



