30 TEMPERATURE AND HEAT 



hearth, the coal which glows in the furnace, and the oil which 

 burns in the stove owe their existence to the sun. 



Without the warmth of the sun seeds could not sprout and 

 develop into the mighty trees which yield firewood. Even 

 coal, which lies buried thousands of feet below the earth's 

 surface, owes its existence in part to the sun. Coal is simply 

 buried vegetation, vegetation which sprouted and grew under 

 the influence of the sun's warm rays. Ages ago trees and 

 bushes grew " thick and fast," and the ground was always 

 covered with a deep layer of decaying vegetable matter. In 

 time some of this vast supply sank into the moist soil and 

 became covered with mud. Then rock formed, and the rock 

 pressed down upon the sunken vegetation. The constant 

 pressure, the moisture in the ground, and heat affected the 

 underground vegetable mass, and slowly changed it into coal. 



The buried forest and thickets were not all changed into 

 coal. Some were changed into oil and gas. Decaying ani- 

 mal matter was often mixed with the vegetable mass. When 

 the mingled animal and vegetable matter sank into moist 

 earth and came under the influence of pressure, it was slowly 

 changed into oil and gas. 



The heat of our bodies comes from the foods which we eat. 

 Fruits, grain, etc., could not grow without the warmth and 

 the light of the sun. The animals which supply our meats 

 likewise depend upon the sun for light and warmth. 



The sun, therefore, is the great source of heat ; whether it 

 is the heat which comes directly from the sun and warms the 

 atmosphere, or the heat which comes from burning coal, 

 wood, and oil. 



