Slike stranica

control the growth of plants are all that he has to concern himself with. The main auxiliary for this is furnished in the botanical garden, where the eye sees the products of all localities, arranged, according to their grouping, in the countries where they are indigenous. Botany and zoology and mineralogy are among the sciences most valuable in throwing light upon geography; they display best what wealth each country holds in store for the uses of man; for they are closely connected with the development of industry, the arts, and trade.

This brings us to the last province, commerce, the science of interchange. The study of minerals, of the distribution of plants and animals, is of little advantage, aside from commerce and its uses to man. It is the interchange of the products of one region for those of another which has had, on the whole, the greatest influence on the human race. Think, for an instant, of the transfer of the potato from America to Europe, of maize to Asia; of the far more ancient introduction of wheat and rice from Asia into Europe; and not these alone, but almost all the fruits. Think of the carrying from Asia to America, and, in fact, to all tropical lands, such products as sugar, coffee, and cotton. Think, too, of the results of the search for gold, ivory, and slaves in the interior of Africa, and of gold in California and Australia, opening such immense districts to settlements. The search after platina has disclosed the most guarded recesses of the Cordilleras and the Ural chain; while the need of copper first gave us our complete knowledge of the great system of American lakes. Without the expeditions to secure the whale, the walrus, and the seal, as well as the fur-bearing animals, the polar world would be still untraversed. The discovery of coal on a hundred shores otherwise unknown, led to the settlement of man in colonies from India and China southward to the Antarctic Continent, and northward to Nova Zembla, Spitzbergen, and Greenland. And not the continents only, seas and oceans have been thoroughly studied, in order to secure a safe pathway for man to the regions which contain his spoils. In the furtherance of this, the highest praise must be awarded to the British government. Through its enterprise and liberality, almost every island group has been examined, a thorough study of marine currents undertaken, careful soundings made in all waters, and a most extensive chartography C*

accomplished. The charts published by the English admiralty already are counted by thousands.

Yet the French have not been backward in like investigations. Understanding the value of commerce, their Dépôt de la Marine has not been inactive. Scandinavia has also done her part. The United States has accomplished one of the most thorough coast surveys ever undertaken by any nation; its difficulties are only to be measured by its extent. In fact, the whole civilized world has sent its messengers to the ends of the earth, and have united in this grand crusade of our age, the enriching of all men by a liberal system of interchange of the commodities of all climes.




The Spheroidal Form of the Earth.

THE measurements of, and investigations into the figure of the earth, have led, as already stated in the introduction, to no absolutely certain conclusion; yet they have made it certain that the earth is, in a general sense, a spheroid. There are many discrepancies, as were then stated, from the perfectly spheroidal shape; still it is in this sense a spheroid, that the polar diameter is not of the same length with the equatorial diameter.

The globular form of the earth, using that word in a loose sense, has been established with certainty since Newton's time. The experience of circumnavigators, the uniform shield-shape of the shadow of the earth during eclipses of the moon, are witnesses to this. The gradual emerging and disappearance of objects, such as ships on the sea, in coming and going, caravans on the desert, of mountains as they are approached, establish the fact. These proofs are so well known that we but touch on them and pass to what is not so obvious.


As soon as the fact was established that the earth was a subordinate member of a system, it was brought into analogy with other planets, and their uniformly spherical shape was considered another valid reason for attributing the same to our globe. The discovery of the rotation of the earth on its axis was still another argument in the same direction. Mathematical measurements and observations of the pendulum, taken at different stations, have confirmed the same result.

To measure a spherical body, it is only necessary to take the length of a degree in one of its great circles, and to multiply its length by 360, the number of degrees. The method of measuring a degree on the earth's surface is by taking two stars, just one degree apart, dropping, by astronomical and mathematical means, vertical lines upon the earth from them and measuring the distances apart of the points where those lines impinge upon the globe. This can be done with perfect accuracy. Such investigations show that the degrees are not all of equal length, as they would be were the earth a perfect sphere. Nearer the poles they are longer, nearer the equator they are shorter. The curvature of the earth is therefore greater as you approach the equatorial line, and less as you recede from it. In general terms, then, the earth is an oblate spheroid, as it would be a prolate spheroid were the lengths of its diameters reversed. By the most accurate measurements, those of the astronomer Bessel, if the equatorial diameter were divided into 289 equal parts, the polar diameter would measure 288 of them, being o shorter.

To this must be added what was said in the introduction, that the surprising accuracy of modern instruments and modern investigations, applied to meridian circles and parallels of latitude, have determined the fact that the

spheroid is not a perfect one, (just as so often in nature the ideal is rather striven after than attained,) but an irregular polyhedron of an indeterminate number of sides. Still for all practical purposes, these minute inquiries have no value, and it is enough to treat of the earth as a perfect globe, so far, at least, as map-drawing is concerned. The deviation from a perfectly spherical shape is so inconsiderable that in an artificial globe of eighteen inches diameter it would hardly amount to the thickness of a sheet of paper; still, small as this is represented on a miniature scale, it has, doubtless, great importance on the great scale of a world like this, both in affecting somewhat the perturbation of other heavenly bodies which depend on the earth, as well as the perturbations in the earth's own motion. Besides this, which is really not a small point in consideration of the possible results which the minutest perturbation of one little planet may have on the universe, there is one other, more appreciable in its results, the probable influence of this spheroidal, or rather polyhedrous form, in producing the unequal division of land and water upon the surface of the earth. The apparent want of any principle or reason for this inequality has long perplexed geographers, and there seems to be no more satisfactory solution than the one to which I have just alluded. In the course of future investigations into the yet undetermined exact mathematical form of the earth, the law which controls the division into land and water will be more thoroughly understood. Unquestionably the position of the great oceans depends upon their distance from the center of the globe, and although the present proportion of land and water seems fortuitous, undoubtedly it has a uniformly acting, and a thoroughly appreciable law.

« PrethodnaNastavi »