Page:Mars - Lowell.djvu/200

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MARS

These lines, important in navigation, are in reality diminishing corkscrew-like spirals, but on this projection become straight lines which can be instantly laid down by rule and compass. To make such delineation possible it is necessary to distort the proportions of every part of the map, in increasing divergence toward the poles, with the lamentable result that in early life we all believed Nova Zembla to be a place as big as South America. Nevertheless Mercator's projection has certain advantages not so obvious to the uninitiated, nor requiring special mention here. In this connection it is only necessary to warn the reader, in the case of a geography with which he is not familiar, like that of Mars, to remember that the top and bottom of the map are drawn upon a scale three or four times as large as the middle; and, furthermore, that it is a consequence of Mercator's projection that arcs of great circles appear upon it, not as straight lines, but as curves always more or less concave to the equator. For relative size of the various features, he will find the twelve views from the globe accurate; but for the impressiveness of the great circle character of the canals, nothing short of a globe itself will give him adequate realization.

The map represents that part of the planet lying between latitudes 70° south and about 40° north. The south circumpolar regions will