Page:Popular Science Monthly Volume 16.djvu/521

Rh details were so enormous that the work of giving the whole of the surface of the earth, as far as known, with all the details of continents, oceans, gulfs, bays, straits, rivers, mountain-ranges, and islands, with any marked approximation to correctness, was not accomplished until Mercator produced his great map of the world in 1569; which, when the fullness of its details is considered in connection with the new and scientific method upon which he projected it, entitles him to the appellation of the father of modern cartography. In this map he introduced what has ever since been known as Mercator's projection, which not only gave the world in one view, but by an ingenious and simple contrivance showed the most effectual way for a vessel to sail in a straight line over a curved surface, and thereby solved what was before one of the most difficult problems in navigation. That projection constitutes, down to the present day, the basis of every chart that is constructed to guide the mariner in his way over the ocean, and the map of the world on his projection is to be found in nearly every English or American atlas that has been published for a century and more, and yet the inquirer would search in vain in any work in the English language for the particulars of Mercator's life, or for any satisfactory account of what he did. How little is known respecting him, even by nautical men, will be sufficiently indicated when I state that, upon speaking about him not very long ago to a distinguished admiral, he looked at me and exclaimed: "What! was there such a man as Mercator? I always supposed Mercator's projection meant the merchant's projection."

 

HE separation of a liquid from solids suspended in it, by straining through some material pervious to the one and impenetrable to the other, was a familiar process in the remotest antiquity. Observation of various processes in nature, such as the purification of water by trickling through sandy soil, or perhaps the accidental passage of rain-water through an outstretched cloth, a garment, or a tent-cover, would obviously suggest the simple expedient. History fails to record the period of the invention or the name of the individual who first put it in practice. Etymological considerations show that filters were early made of fulled wool or felt; the Latin filtrum, "a filter," being closely connected with feltrun, "felt," or compressed wool, and both are related to the Greek πιλος, signifying hair.

Several writers on the history of science make casual reference to 