404 THE POPULAR SCIENCE MONTHLY. 



per cent, of the rainfall upon their surface." It follows that any nat- 

 ural exposed basin, under these circumstances, would surely fill up, 

 just from the rains on its surface, if there were not some outlet for the 

 water. Mr. Fanning gives the mean annual rainfall at Fredonia, New 

 York, a few miles from Lake Chautauqua, as 36*55 inches. If we 

 assume that the lake has an area of forty square miles, and take the 

 annual rainfall on its surface at three feet in depth, the total volume 

 of this rainfall would be 3,345,408,000 cubic feet. Supposing that 

 sixty per cent, of this is lost by evaporation, there will yet remain in 

 average years 1,338,163,200 cubic feet of water to be somehow disposed 

 of, which is more than would supply a stream eight feet wide and one 

 foot deep, running for a year at the rate of three and a half miles per 

 hour. Besides the rain falling directly on the surface of the lake, a 

 calculation of the area of the land around it, at a higher elevation than 

 its water-level, would undoubtedly show, no matter what unpracticed 

 observers might anticipate, that the rain-water known to fall on this 

 area would be ample to supply all the springs that flow into the lake, 

 and leave a good margin of surplus to evaporate from plants and soil, 

 and to filter away into the earth. 



It seems as if Mr. Gi-een must be somewhat imaginative when he 

 says that, " from the highest mountains in the world — the Himalayas 

 — out of their highest points, great cataracts and streams have poured 

 and still do pour," etc. Has any man ever been anywhere near the 

 highest points of the Himalayas to verify such a statement ? I trans- 

 late the following from Arago's work already mentioned : 



" The argument chiefly depended upon by those who felt obliged 

 to seek the origin of subterranean waters in the precipitation which 

 intensely hot aqueous vajjors, coming from central regions, had expe- 

 rienced at the moment of their contact with the cold, earthy layers 

 near the surface, was drawn from a fact well worthy of examination : 

 I mean the pretended existence of tolerably abundant springs at the 

 summit, at the culminating point, of some mountains. Our little 

 Montmartre itself figured in this polemic. There was, indeed, upon 

 this hillock, a spring (perhaps it still exists) which was hardly sixteen 

 metres (fifty feet) below its highest part. No water, it was said, could 

 constantly feed a spring thus placed, without coming from beneath in 

 the state of vapor. Upon examination, however, it was found that 

 the portion of Montmartre above the spring, and which could conse- 

 quently transmit its waters by the method of simple interior draining, 

 was about five hundred and eighty-five metres long and one hundred 

 and ninety-five metres wide. Now, the mean volume of rain which 

 falls in Paris upon such an extent of ground, between the 1st of Janu- 

 ary and the 31st of December, much exceeds the quantity of water 

 which the little spring in question annually yielded. 



"It was necessary, then, to seek for the difficulty at another 

 point. 



