30 



Refervoirs not 



(applied. 



Divided refer- 



A lock filled 



from a canal. 



Velocity of a 

 river confidered 



SUMMARY OF HYDRAULICS. 



For prifmatic veffels, all the particulars of the difcharge may 

 be calculated from the general law that twice as much would 

 be difcharged from the fame orifice if the vefTel were kept full 

 during the time which is required for its emptying ilfelf. 

 (Young's Syllabus, 245). Where the form is lefs fimple, the 

 calculations become intricate, and are of little importance. 



Chapter 6. Of the difcharge from compound or divided 

 refervoirs. 



The author obferves from Buat, that the difcharge through 

 an orifice between two refervoirs, below the furface, is the 

 fame as if the water ran into the open air. Hence he calcu- 

 lates the difcharge when the water has to pafs through feveral 

 orifices in the fides of as many refervoirs open above. In fuch 

 cafes, where the orifices are fmall, the velocity in each may be 

 confidered as generated by the difference of the heights in the 

 two contiguous refervoirs, and the fquare root of the difference 

 will therefore reprefent the velocity; which muft be in the 

 feveral orifices, inverfely as their refpecYive areas; fo that we 

 may calculate from hence the heights in the different refervoirs 

 when the orifices are given. Mr. Eytelwein thenconfiders the 

 cafe of a lock which is filled from a canal of an invariable 

 height, and determines the time required, by comparing it 

 with that of a veffel emptying itfelf by the preffure of the 

 water that it contains, obferving that the motion is retarded in 

 both cafes in a fimilar manner; and he finds the calculation 

 agree fufficiently well with experiments made on a large fcale. 

 The motion of water through different compartments of a doled 

 cavity is alfo determined. 



Chapter 7. Of the motion of water in rivers. 



The fimple theorem by which the velocity of a river is de- 

 termined, appears to be the mod valuable of M. Eytelwein's 

 improvements ; although the reafoning from which it is deduced 

 is fomewhat exceptionable. The friction is nearly as the fquare 

 of the velocity ; not becaufe a number of particles proportional 

 to the velocity are torn afunder in a time proportionally fhorr, 

 for according to the analogy of folid bodies, no more force is 

 deftroyed by friction when the motion is rapid than when flow, 

 but becaufe when a body is moving in lines of a given curva- 

 ture, the deflecting forces are as the fquares of the velocities 

 (Young's Syllabus, 40, 35, 4-6), and the particles pf water in 



contact 



