GEORGE.  “Do you know the cause of these regular winds, papa?  You say learned men try to discover why such things are so, and generally find out causes from their effects.”

MR. WILTON.  “Exactly so, my boy; and learned women do the same:  as an instance, I will quote the learned Mrs. Somerville on this very subject, and give you an excellent reply to your question.

“’The heat of the sun occasions the trade-winds, by rarefying the air at the equator, which causes the cooler and more dense part of the atmosphere to rush along the surface of the earth to the equator, while that which is heated is carried along the higher strata to the poles, forming two currents in the direction of the meridian.  But the rotatory velocity of the air corresponding to its geographical situation, decreases towards the poles; in approaching the equator it must therefore revolve more slowly than the corresponding parts of the earth, and the bodies of the surface of the earth must strike against it with the excess of their velocity, and by its reaction they will meet with a resistance contrary to their motion of rotation; so that the wind will appear, to a person supposing himself to be at rest, to blow in a contrary direction to the earth’s rotation, or from east to west, which is the direction of the trade-winds.’”

GEORGE.  “May I read that to-morrow, papa?  I do not quite understand it; and if you have the book, I could read it over and over until I found out the meaning.”

MR. WILTON.  “You will find it in Mrs. Somerville’s ’Mechanism of the Heavens.’  If you come to my study to-morrow morning before I leave home, I will assist you in the solution of the difficulties.”

MR. BARRAUD.  “In an account of Cabul I have read a fine description of the commencement of a monsoon:—­’The approach is announced by vast masses of clouds that rise from the Indian Ocean, advancing towards the north-east, gathering and thickening as they approach the land.  After some threatening days, the sky assumes a troubled appearance in the evening, and the monsoon sets in generally during the night.  It is attended by such a violent thunder-storm as can scarcely be imagined by those who have only witnessed the phenomenon in a temperate climate.  It generally begins with violent blasts of wind, which are succeeded by floods of rain.  For some hours lightning is seen without intermission:  sometimes it only illuminates the sky, and shows the clouds near the horizon; at others, it discovers the distant hills, and again leaves all in darkness; when, in an instant, it reappears in vivid and successive flashes, and exhibits the nearest objects in all the brightness of day.  During all this time the distant thunder never ceases to roll, and is only silenced by some nearer peal, which bursts on the ear with such a sudden and tremendous crash, as can scarcely fail to strike the most insensible heart with awe.  At length the thunder ceases, and nothing is heard but the continued pouring of the rain and the rushing of the rising streams.’”