THE ROMANCE OF THE EARTH.

Lyttelton Times, Volume XCIX, Issue 11538, 26 March 1898, Page 2

THE ROMANCE OF THE EARTH.

[By Professor Bickerton.] I. . ’ A massive globe, about 8000 miles through, is rushing forward in space at the ■ rate of some twenty miles a second. The globe is nearly as heavy as though it were solid iron, and its speed is about fifty thnes : that of a cannon ball. A piece of this'; globe equal in weight to a cannon ball would strike a blow of two thousand times, its energy. Were this globe alone it would, travel straight on in space. Its motion 1 would be more direct than that of a rifle ball, for the latter moves in a curve and. always tends to fall towards the earth. Our giant globe has a companion more than a million times its own size, and, like the rifle ball, it tends always to fall towards the larger body, ■ and so it also moves in a curve. This tremendous projectile is the earth, and its gigantic companion is the sun. The curve which the earth moves in is almost ‘h circle, what geometricians call an ellipse, and our globe takes a year to complete its round. Sometimes it falls a little out of its circular course, towards the sun. ahd thd tremendous pull makes it get up speed, just as a great snowball accelerates itself: in rolling down hill. Presently the speed—and consequently the centrifugal force—is so great, that the pull of the sun is unable to draw the earth nearer; it is, as it were, at the bottom of the hill; and then" it gradually loses speed; it climbs up another, hill, so to speak,. until it gets to its maximum distance from the sun —about 93,000,000 miles. After its headlong rush down hill, it is about 2,000,000 miles nearer. This difference is not always the- same. Sometimes there is as much as 13,000,000 miles difference; and then come into action wonderful agencies which clothe much of one hemisphere with ice, a great glacial period converting temperate countries into arctic. As the earth spins onward in space it rotates, and when one side faces the sun it is there day, and when it is away from the sun‘ it is there night. If we think of the curve in which the earth revolves as a hoop floating in still' water, we may call the surface of the water the ecliptic; and if. we imagine our glebe a spinning globular top dipping halfway through the hoop, its axis will appear not upright but tipping, over a good deal. If it tipped over four times as much, its axis would lie on the surface of the water. This surface is called the ecliptic, because it is when the moon is in this plane that we have eclipses. The moon is a body about fifty times less than the earth, and it revolves around the earth in twenty-eight days. Its orbit, that is, the circle it travels in, does not lie in the ecliptic, otherwise the moon would get between us and the sun much more--fre-quently than she does—every new moon we should have an eclipse of the sun. A fortnight later the moon would be immediately behind the earth, and away from the sun, and every full moon we should have a lunar eclipse. The moon’s orbit dips slantwise through the plane of the ecliptic, and so it is occasionally only that the sun, moon and earth lie .in a straight line, and we have an eclipse. The fact that the earth spins with a leaning axis causes the seasons. If its axis tipped right over into the ecliptic, at one time the sun would blaze square upon one pole ; and, six months later, square upon the other. But, as it leans a little only, at times the sun shines slanting upon one pole, and six months later it shines upon the other pole, and we have the arctic and antarctic summers. Nearing the equator we come' to a point where at midsummer the sun shines directly over-; head. The most northern circle traced; round the earth by this vertical sun we call the Tropic of Cancer. Sonfetimes great pillars are built and deep wells are dug on this circle, and when the pillar casts no shadow, or the sun blazes directly to the bottom of the well, it is twelve o’clock on midsummer day. Many snch pillars are of great antiquity, showing. tha,t the ancients were- acquainted with some of the important facts of astronomy. Midsummer day being past, the vertical sun gets nearer and hearer to the equator, and iu three months it is overhead at the equator, and we say the earth is at its equinox; for all over the globe the days and nights are equal. Another three' months elapse, and the southern limit of. the vertical sun is reached, the Tropic of Capricorn. In three months the sun is back again to the equator; so we sea that, the equator has two summers a year, and everywhere within the tropics the sun is vertical twice a year. The earth and its moon are not the only companions, of the sun; there are seven other true; planets, four small ones near the sun, and four large distant ones. The two sets are divided by a belt of hundreds of little planetoids. The earth is the third planet ■ reckoning from the sun. Mahy of the peculiarities of the planets have been described iu “ A New Story of the Stars.” On the earth, within the tropics, the heat of the vertical sun causes great evaporation, and this moisture, being carried upwards by currents of ascending i heated hair, is chilled by expansion at extreme altitudes, and descends as rain. These tropical torrents, combined with the heat, result in a profuse vegetation, along with which predatory beasts, reptiles, gorgeously-plumaged birds, and wondrous insects, give an aspect of luxuriant growth and teeming animation. The poles, on the contrary, are covered with perpetual ice, and there is almost no life there. At the pole, the sun is below the horizon for six months • then its upper limb circles round, showing, itself between the hills in the low valleys. Next, more of the disc appears, ,then'it circles completely round the horizon. (Jetting above the-bills, it travels slowly upwards in a continuous spiral till it reaches an angle of 23|deg from the horizon;. then it spirals down again, ever in sight save when some cloud obscures it. Thus, for six months, there is no night, and a scanty vegetation struggles into brief life. Leaving the pole, w 6 come to a circle on the globe where, at midsummer only, the sun may be seen continuously for twenty-four hours, giving us “ the midnight sun.” This we call in the north the Arctic Circle, in the south the Antarctic Circle. Then, travelling towards the tropics, the inequality between summer and winter gradually decreases, so that between northern New Zealand and northern Britain the climatic contrast is great, the summer and winter days of Auckland being much more equal than those of Scotland. Even iu New Zealand itself the long summer evenings of Invercargill are very different from the early nightfall of Auckland midsummer. Of course, at the equator- the days and nights are always of equal duration.

(To be continued.)