156 The Great World's Farm 



warming the air, loads it with moisture; so that it is easy 

 to understand why the winter climate of Ireland should be 

 mild enough to allow of myrtles flourishing out of doors, 

 and yet why the summer heat should not be sufficient to 

 ripen certain fruits, owing to the thick veil of vapor which 

 screens it from the sun. 



Other local circumstances which affect climate in a 

 greater or less degree are the presence of forests, rivers, 

 lakes, mountains, which cannot now be dealt with in 

 detail. 



But plants are also affected in a minor degree by the 

 color of the soils in which they grow. 



Dark substances absorb more heat than light ones do; 

 and snow will melt more quickly if a piece of black cloth 

 be stretched above it, even though the two do not touch 

 one another. In the Arctic regions the ice melts much 

 faster wherever a small, dark brown plant, of the same 

 family as the red snow, grows, because it attracts the 

 heat. So, too, in some parts of Switzerland the peasants 

 hasten the departure of the snow by strewing it with black 

 powdered slate. 



Dark soils are, therefore, usually warmer than light 

 ones; and it is not an uncommon thing for gardeners to 

 sprinkle a light colored soil with peat, charcoal, or vege- 

 table mold to warm it, for these all act as sun-traps. 



Melons are thus ripened, even in the coolest summers, 

 at Freiberg, in Saxony, by means of a layer of coal-dust. 



Grapes, too, in the Rhine district, ripen best where the 

 ground is covered with fragments of black slate; and the 

 vines are purposely kept near the ground, that they may 

 have the full benefit of the heat which the slate absorbs by 

 day and gives up again by night. 



