THE SEASONS. In our Glimpses of the Wonderful last year, there was a chapter on Astronomy, which contained a brief account of the motions of the heavenly bodies, the comparative sizes of the planets in our solar system, and an allusion to the cause of the changes in the seasons. * Now, lest this last subject should not be fully understood, we had better pursue it a little further, and shall be assisted in our inquiries by the accompanying diagram, intended to show the earth's position with respect to the sun at different portions of the year. Why, then, should the sun give more heat to any particular portion of the earth-say to our island of Britainat one time of the year than it does at another? What makes it so cold here in December and January, and so warm in July and August? It might, perhaps, be supposed that the earth is nearer to the sun in summer, and further off in winter; but, on the contrary, astronomers * Page 142. have proved that we are actually nearly three millions of miles further off the sun at our hottest portion of the year than we are at our coldest. 66 Our former volume briefly alluded to the reason in these words :—“ Some of the planets do not move round the sun in a perfectly even plane, but a sloping one," &c., &c. "This causes the difference of the seasons, without which there would be neither summer nor winter, but the year would be all alike." Now, look at the diagram? There is the sun in the centre, while round him, "On her smooth axle spinning, sleeps the earth." Now this axle, of course, is not a real pole stuck through the earth like a knitting-pin through a ball of worsted, but is merely the term used to describe the part of a revolving body round which it turns itself. Now, we might spin an ivory ball on a smooth, level table in such a manner that it would not leave the spot on which it was first placed, but would keep turning there for a longer or a shorter time, in proportion to the impulse first given. In this case the ball would have only one motion-that of revolving on its axis. Again, we might roll the ball from one part of the table to another, in which case the ball would have two motions -one, as before, on its axis, and another from one part of the table to another. It is in this latter way that the planets roll round the sun; but the position of the axis with respect to the orbit, or course round the sun, varies in different planets. Our earth, which has its axis slightly slanted from the perpendicular, turns round once in every twenty-four hours, during which each part of its surface is by turns brought towards the sun's light, and then gradually rolled away from it into the shadow of night. Besides thus turning round on its axis, it rolls round the sun in a little more than three hundred and sixty-five days—that is, while it is going once round the sun, it turns three hundred and sixty-five times round itself, or, as it was before explained, round its axis. Well, then, we see the axis of the earth (represented by a straight line running from N. to S.) in four positions with respect to the sun. In each of the four positions, N. (or the North Pole) slants towards the right hand, or the East; and S. (or the South Pole) towards the left hand, or the West. Now, when the earth is at D, we may see that the North Pole is slanted away from the sun; when at B. it is slanted towards him, and the South Pole the contrary in each case. At A and C each pole receives an equal portion of the sun's light during the day, and is equally in darkness for the night; the night and the day being at these two periods of equal length, namely, twelve hours each, all over the world. Now, we all know that in England, during the latter part of June, the days are at the longest: the sun rises soon after three o'clock; at mid-day he is high over head; and he does not disappear till nearly ten o'clock, and it is hardly dark all night. And if, at this time of the year, we went still further north-for instance, to Sweden, we should find the days still longer, and the nights still shorter than in England. Further north still, as in Lapland or Iceland, we should have no night at all, but the sun would continue above the horizon for many days together; that is, for many revolutions of the earth on its axis. On the other hand, at the very same time of the year, namely, the latter end of June, the South Pole is slanted away from the sun, as much as the North Pole is slanted towards it, and instead of there being no darkness there, there is no daylight. Figure B shows the position of the earth with respect to the sun on the 21st of June, which is the longest day in the northern, and the shortest day in the southern hemisphere. On the other hand, the 21st of December is the shortest day in our northern hemi sphere, and the longest in the southern; and, on that day, the earth is placed with respect to the sun as at figure D, with the South Pole slanting towards the sun, and the North Pole away from it. Figures A and C show the position of the earth at about the 21st of March and the 23d of September, when the day and night are equal all over the world, whether north or south of the equator, each being of course twelve hours long. These periods are named the Vernal (or Spring) and the Autumnal Equinox; only, when it is autumn with us, (in September,) and the days are becoming shorter, it is Spring, and the days are becoming longer in South America, at the Cape of Good Hope, in Australia, and New Zealand, and other parts of the southern hemisphere. Now, perhaps, you may have remarked that, in general, the shortest day is not the coldest, nor is the longest day the hottest in the year: according to the old proverb, "As the day lengthens, The cold strengthens." A little reflection will suggest the reason of this. On our shortest day, the sun, besides shining on us for only five hours out of the twenty-four, does not rise so high above us at noon as he does by six o'clock in the morning at midsummer-his rays, instead of pouring down direct |