ANCIENT METHODS OF FILTRATION. 495 



iletails were so enormous that the work of giving the whole of the sur- 

 face 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 

 ^lercator produced his great map of the wox'ld in 1569 ; which, when the 

 fullness of its details is considered in connection with the new and sci- 

 entific method upon which he projected it, entitles him to the appella- 

 tion 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 con- 

 trivance 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 Amer- 

 ican 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 projec- 

 tion." 



ANCIE^TT METHODS OF FILTRATION.* 



Br H. CAEEINGTON BOLTON, Ph. D., 



PROFESSOE OF CUEillSTET IN TRINITY COLLEGE, HARTFORD. 



THE 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. Observa- 

 tion 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 feltrum, " felt," or compressed wool, and both 

 are related to the Greek -rnXog, signifying haii-. 



Several writers on the history of science make casual reference to 

 * Read before the New York Academy of Sciences, October 13, 18Y9. 



