on Rivers and Canals. 631 
velocity of defcent increafes in a compound ratio of the 
increase of the mafs of water, and of the greater declivity 
of the plane which ferves for its bed (N° 13.). 
63. Water, though unaffected by any compreflion or 
impulfion from above, cannot remain immoveable in any 
bed whatever except that which makes a curve perfectly 
concentrical with the terreftrial curve ; but in this, being 
every where equally affected by the force of gravitation, 
it will remain without motion any way. 
64. It follows from hence, that the fprings and fources 
of all rivers mult be at a greater diftance from the center 
of the earth than one femi-diameter thereof, which is 
terminated at the furface of the fea; without which the 
waters could not run to the river’s mouth. 
65. Therefore, the abfolute elevation of the furface 
of rivers is continually diminifhed as they recede from 
their fprings, becaufe of the neceflary declivity of the 
beds of rivers towards the center of the earth ; for with- 
out fome degree of this declivity the waters could not 
run at all, as has been faid above (N° 62. 63.). 
-66. The declivity of the beds of rivers cannot be a 
right line making a rectilinear angle with that horizontal 
plane which, being continued, would interfeCl their re- 
fpedtive fources ; but, if it is regular, it mult, be a curve 
which differs very little from that of the earth’s furface, 
4 N 2 and 
