(448) 
This being fuppofed, it follows, thataVeflel, which contains 
S3 muids of Water , is able to furnifli in twenty four hours fo 
much as will make an I/ich of wa^er run continually. And fo, if a 
Confer vatory fbould hold 3378 w^Wiof water, it would furnifli 
for a whole year a fufficient quantity to make an hch of water run 
conftantly : And if it were as big again, it would m^ke run two* 
and fo on more or lefs in proportion. But here I fuppofe an Equa- 
lity in the running, though 1 am not ignorant, that the Conferva- 
tory being full, the water will then run out with more velocity, 
and confequently in greater quantity, thanwheri 'tis near empty. 
But this being only to make the matter better uuderftood , I (hall 
not ftand upon this precifenefs*- 
But then for the meafure of the Rain and Snow-water , I fliall 
tell you, that as to the Obfervations which I have made my felf of 
thequantity of ftch water, I havefound, that from 0^?<?/'. 1668 
to O^ok 1669, there had fallen fo much of it , as amounted to the 
height of 18 inches 7 lines ; and from the fame Month of 1670 to 
iTie fame Month 1 671, there had fallen only fo much as came to the 
height of Scinches; and froiX) Jamar, 16-73 to Jamar.i 6 j^^ to 
the height of 27^ inches. Of which, taking ihe medium, we have 
19 inches end 2 J lines. 
This fuppofed, we muft for our purpofe meafure or make an 
Eftimat of fome River, as it runs from its very fource to a place 
where fome Rivolet enters into it, and fee, whether the Rain- 
water that falls about the courfe thereof, if it were put into a 
Confervatory, would be fufficient to make it run a whole year. 
I have looked upon and confidered the River of Sewe 'mns 
courfe from the fource of it unto Jimy le Dus, where enters a Ri- 
volet that fwells it* And this I fhall take for the fubjefl of the 
Edcamen 1 intend to niake. 
The courfe then of this River from its Spring to the faid Aiftay 
D^ff is about three leagues 16ng, and the fides of its courfe ex- 
tend themfelves on the right hand and the left about two leagues on 
each fide, where there are other little Rivers that run another way: 
And, (Ince that ttjefe Rivolets need Water ro maintain them as well 
as the Seine^ I will count but half that fpace of thefides,and fay, 
that the place where the Seine pafTes, hath from its fource to Aimy 
le Ducy three miles long, and two miles large. Whereupon I fay 
further, if a Confer vatory were made of thisbignefs, it would be 
fix leagues fquare infurface, which being reduced to fathoms, 
v/O'ld, 
