CHAPTER X.
TRANSPORTATION OF HEAT.
o-day we come to that subject which we should have looked at a week ago, if that I hope not unprofitable discussion of the uses of trials and the ministry of pain had not prevented. We must now examine the arrangement for softening the rigors of winter and toning down the heat of summer. The general principle is that in summer the earth receives an excess of heat, while in winter the opposite is true. These extremes are mitigated by transferring heat from summer to winter. How is this accomplished? Any one who has thoughts upon this subject may answer.”
“I have some thoughts,” said Ansel, “but whether right or wrong, I cannot tell. I should think heat might be carried from summer to winter in the same way as from day to night.”
“What are some of those means for transferring heat which seem to you to operate the same in the annual as in the daily changes of temperature?”
“One is the absorption and radiation of heat, and another is the evaporation of water and the condensation of vapor.”
“You are right,” said Mr. Wilton. “The effect of these operations in the equalization of the annual extremes of heat is in no wise different from their effect upon the temperature of day and night, but from summer to winter their effect is vaster and more impressive. During the summer, sea and land, and ‘all that in them is,’ are receiving heat and rising in temperature. The heat of summer penetrates and warms the earth nearly a hundred feet in depth. Into the sea heat penetrates still deeper. How vast the amount of heat required to warm the whole surface of the earth and sea to such depths! By withdrawing so much heat from active use the intensity of the summer temperature is softened. During the colder months the land and sea slowly radiate their heat. We can hardly over-estimate the effect of this alternate absorption and radiation of heat. So great is the effect of this stored up heat that the sea and the great lakes never freeze even in the coldest winter weather, except in the polar regions, and the temperature must fall far below freezing and continue for a long time below the freezing point before the earth begins to freeze. The great bodies of water, remaining always at a temperature above thirty-two degrees, are especially important in warming the wintry air. In the coldest weather they seem like steaming caldrons throwing up their warm vapor. It is the absorption and radiation of heat alone which prevent the temperature of the atmosphere from rising or falling suddenly to the highest or lowest point possible. The sun breaks forth in all its splendor at noonday in summer: what if the sun were to remain stationary, shining thus in his strength for days and months? Everything would be consumed with heat. But why do not the glowing rays of the sun raise the temperature at once to the highest possible point? Because the earth and sea and every object upon the earth absorb the heat, storing it up and holding it in reserve. On the other hand, when the sun sets and his heat is withdrawn, why does not the temperature fall suddenly to the lowest possible point? Because the heat held in store is slowly radiated and the change of temperature rendered gradual.