The ascertaining of superficial areas with exactness is one of the most costly operations undertaken in the interest of science. The first mathematical survey of France, one hundred and fifty years ago, undertaken by Cassini, cost four millions; the second sixteen millions; a third, still more costly, has been made within the present century. Still, it must be said that few countries have expended money in this direction with as much prodigality as France. In Turkey, for instance, so little accuracy has been attained, that the survey of that country, undertaken by Beauchamp early in this century, resulted in establishing the Sultan in possession of 17,000 square miles which he had supposed were covered by the Black Sea. The recent surveys of Prussia have rectified similar mistakes, and, in the constantly increasing accuracy, have given hundreds of square miles to the Crown. Many countries, and in truth the most, have never been subjected to a strict mensuration. The jagged coast lines of islands and continents have been so great a barrier, that we have to speak with great uncertainty of the superficial contents which they inclose. The statements of these make no pretense, therefore, to accuracy. We must be content, at present, with the rudest approximation. This accounts for the discrepancy in our geographical compendia; no two of them agree, unless one servilely copies the other. The statistics relating to the superficial contents of continents, and of separate countries, must be taken with a great deal of allowance. The evil cannot be remedied at present; it will be, doubtless, at some future day. The discrepancies which it occasions will be seen, from the fact that the area of Europe has been computed to be between 3,254,800 and 3,870,500 square miles; that of Asia between 16,180,000 and 16,831,600; that of Africa between 11,257,200 and 11,513,600; that of America between 12,140,400 and 15,963,600; that of Australia between 2,756,000 and 3,201,200 square miles. According to this, Asia is five times as large as Europe, and almost six times as large as the continent of Australia. Africa is three times as large as Europe. America is four times as large as Europe, and is as large as Africa and Australia combined. Europe would make about one-third of Africa, one-quarter of America, one-fifth of Asia. Our present knowledge does not allow us to speak more definitely nor exactly. Contrast of the Land and Water Hemispheres. Whether we divide the globe into northern and southern or eastern and western hemispheres, their relative amounts of land and water will be different The northern hemisphere contains (speaking approximatively as above) 38,541,600 square miles of land, and 59,619,700 of water; the southern, 12,847,200 of land, and 85,526,100 of water. The eastern hemisphere contains 36,760,800 square miles of land, and 61,401,000 of water; the western, 14,628,000 of land, and 83,533,300 of water.