"Your question is an important one, and deserves an answer. For myself, I look upon the fact to which you refer as one of the many points in which this world is adapted to human needs. Man is put in a condition which requires boundless thought and toil for the supply of his higher wants just because he possesses a nobler nature and such thought and exertion are needed for its development. Which is the more desirable condition for a young man to be placed in--one in which his every wish is anticipated and his every aspiration is gratified without exertion on his own part, or one in which opportunity and means are furnished for self-help, one in which he can supply his wants and satisfy his aspirations only by the exercise of his best abilities? Which will encourage the larger manliness and nurture the higher culture and strength? He who has no need for exertion rises at best only to a soft and feeble luxury, without mental vigor or moral force. What does man need besides scope and reward for exertion? Effort and struggle are necessities of our nature. This is especially true of man's higher faculties. Human greatness and goodness are not created by a word: they must be developed by exertion. For this reason God has made exertion necessary, and as much more necessary with man than with the brutes as his culture is more the result of voluntary, intelligent exertion. Does this explanation seem to you satisfactory, Mr. Hume?" "I have no fault to find with it; I must think of it." "Very well, then; if no other one has a question to ask, we will look at another subject. We will survey the storehouses of heat which God has prepared for warming the earth. Samuel, you may name the first great source of heat." "I think, sir, that the sun is the chief source of heat." "We certainly receive the larger part of our heat from the sun. No one can doubt this. So much of our heat comes from the sun that the temperature of the earth varies according to the sun's heat, as if that were the only supply. If but a fleecy cloud pass between the sun and the earth, we feel a decided change of temperature. A few hours less of sunshine each day, and a few degrees more of inclination to the sun's rays, change summer to winter and make the difference between the torrid and the frigid zones. Withdraw the heat of the sun altogether, and the whole world would become a desert of frozen death." "What is the cause of the sun's heat?" asked Peter.