470 Conftriittion of [Book VII, 



tain declivity fhould have their floats or buckets in- 

 clined fo much towards the radius as to caufe them 

 to be ftruck in a more perpendicular direction, that 

 they may receive an augmentation of force from, 

 the weight of the water. The moft advantageous in- 

 clination of the floats towards the radius appears by ex- 

 perience to be between twenty and thirty degrees. 



A wheel placed near a refervoir turns fwifter than 

 in any other place, becaufe then the whole force of 

 the defcending fluid is effectually applied; but if there 

 is a neceffity for placing it at the end of the water- 

 courfe, at a certain diftance from the refervoir, the 

 channel of the water- courfe or frame fhould incline 

 about the tenth part of its length, fo that the Hoping 

 may give to the water that degree of velocity which 

 would otherwife be deftroyed by friction ; the wheel 

 will then receive the fame impulfe as if it was placed 

 clofe to the refervoir. 



Water acting by its weight produces a much greater 

 effect than when it acts by its fhcck in falling. M. 

 Parent, in the year 1704, and M. Pitot, in 1725, in- 

 deed demonftrated, that a wheel (fuppofed to be with- 

 out friction) moved by a current of water, and de- 

 figned to elevate a portion of that water to the height 

 of that which puts it in motion, is incapable of ele- 

 vating it higher than -/ T or ^ nearly; whereas the water 

 acting upon the wheel by its own weight would be 

 capable of elevating to the height from which it de- 

 fcended half of the water which defcended. 



When, therefore, we have only a fmall quantity of 

 water, and are obliged to hufband it well (which often 

 happens, becaufe there are more fmall ftreams than 

 large rivers) we fhould contrive to make this water 

 act by its weight rather than by its fhock or impulfe ; 

 for this purpofe, inftead of having wheels with plain 

 i float- 



