Part I. 

 chanics. 



OQ SUMMARY OF HYDRAULICS. 



efpecially fuch as are the mod capable of practical application ; 

 and he appears to have done this in To judicious a manner, as to 

 make his book a moft valuable abftrad of every thing that can 

 be deduced from theory refpetting natural and artificial hy- 

 draulics. This elegant concifenefs defer ves fo much the more 

 praife, as his countrymen in general appear too often to make a 

 merit of prolixity; and we (hall have occafion to remark, that 

 befides the convenience of fimplicity, he has fometimes been 

 fortunate enough to unite with it the advantage of fuperior 

 accuracy. 

 Me- The firfl part of the work is but fliort ; it relates to proper 

 mechanics, and has little that is remarkably new or interefting. 

 In treating of pendulums, the author informs us, with reference 

 to another work of his own, that the Rhinlandor Brandenburg 

 foot contains 1.39.13 French lines. Hence it appears that 

 100 Rhinland feet are exactly 103 Englifh ; and in this paper, 

 the meafures will be reduced accordingly. 



The fecond part, relative to hydraulics, contains befides a 

 fliort introduction, twenty-four chapters, almofl every one of 

 which prefents to us fomething of importance. 



Chapter 1. Of the motion of water flowing out of refervoirs, 

 and of the contraction of the Itream. 



§ 89. The velocity of water flowing out of a horizontal 

 aperture, is as the fquare root of the height of the head of 

 water. 



That is, the preflure, and confequently the height, is as the 

 fquare of the velocity : for the quantity flowing out in any fliort 

 time, is as the velocity; and the force required to produce a 

 velocity in a certain quantity of matter in a given time, is alfo 

 as that velocity ; therefore the force mull be as the fquare of 

 the velocity. The propofition is fully confirmed by Boflut's 

 experiments ; the proportional velocities, with a preflure of 

 1, 4, and 9 feet, being 2722, 54-36, and 8135, inftead of 2722, 

 5444, and 8166; a very inconfiderable difference. 

 Another devc- There is another mode of confidering this propofition, not 

 lopement. mentioned by Eytelwein, which is a very good approximation. 



Suppofing a very fniall cylindrical plate of water immediately 

 over the orifice, to be put in motion at each inftant by means 

 of the preflure of the whole cylinder {landing on it, and fup- 

 pofing all the gravitation of the column to be employed in ge- 

 nerating the velocity of the fmall cylindrical plate, neglecting 

 4 its 



Part 2. Hy- 



draulics. 



Water ifiVing 

 from refervoirs, 



Law of its velo- 

 city : As the 

 fquare root of 

 the height. 



