VOL. X.] PHILOSOPHICAL TRANSACTIONS. 243 



24- lines. This supposed, we must for our purpose measure, or make an esti- 

 mate, of some river, as it runs from its very source to a place where some rivu- 

 let enters into it, and see whether the rain water that falls about its course, if it 

 were put into a large reservoir, would be sufficient to make it run a whole year. 



I have observed the River Seine, in its course from the source of it unto 

 Ainay le Due, where a rivulet enters that swells it. And this I shall take for 

 the subject of the examination I intend to make. — ^The course then of this river, 

 from its spring to the said Ainay le Due, is about three leagues long, and the 

 sides of its course extend themselves on the right and left about two leagues on 

 each side, where there are other little rivers that run another way : and since 

 these rivulets require water to maintain them, as well as the Seine, I shall count 

 but half that space of the sides, and say, that the place where the Seine passes, 

 has, from its source to Ainay le Due, three miles long, and two miles broad. 

 So that, if a reservoir were made of this size, it would be 6 leagues square in 

 surface, which being reduced to fathoms, it would according to the measure 

 abovementioned, make 31-^ millions of fathoms in surface. In this conservatory 

 imagine, that during a whole year, there has fallen rain to the height of 19 

 inches 2^ lines, as before said; this height of 19 inches and 2^ lines gives 

 nearly 281 millions of muids of water. — All this water thus collected, in the 

 quantity just now expressed, is that stock which is to serve to make the river 

 run for a whole year, from its source to the place before named, and which 

 must also serve to supply other occasions and losses, such as are the feeding of 

 trees, herbs, vapours, and extraordinary swellings of the river while it rains, and 

 the deviations of the water running another way. 



Concerning the measure or estimate of the water of this rising river, it would 

 be difficult to determine it precisely, as well as what quantity it furnishes. Yet, 

 so far as I was able to judge, it can have no more than 1000 or 1200 inches 

 of water always running, compensating the less quantity it has at its source 

 with the greater it has towards Ainay le Due : which I so judge by the com- 

 parison I make of these waters with those of the river of the Gobelins, in the 

 state of it near Versailles, where it has 50 inches of water, according to the 

 measure taken of it. So that I judge it will be enough to allow 24 or 25 times 

 as much to our river. For the channel of it is to be 4 or 5 fathoms broad, and 

 is but shallow. 



These particulars being thus supposed, then, according to the measures agreed 

 on, 1200 inches of water furnish in 24 hours, after the rate of 83 muids of 

 water to an inch, 99600 muids of water ; hence, in a whole year, which is 

 near 366 times as much, they will furnish near 36-i- millions of muids. This 

 river then sends away within its banks in a year, no more than about 36^ 



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