Tjr)2. the effect of 'xater on machinery. 315 



" Wiere a fall of v/ater can be commanded. But in a 

 a flat country this rule also is reversed ; for where 

 the current is g%ntle,- it is a rule without exception, 

 that the broader the wheel is, or in other words, the 

 longer the float-boards are, with the greater force 

 will the water act upon machinery as a moving 

 power. 



Inall cases of this kind, also, the wheel, for obvi- 

 ous reasons, ought to be made of as large a diameter as 

 ■ can be conveniently done. 



In fliort the float-boards ought to be of such a length, 

 as to go acrofs the whole breadth of the stream ; and 

 were it ten, twenty, or thirty feet in breadth, the 

 wheel ought to be of the same breadth, having sup- 

 ports for the axle at each side of the river. 



Where the breadth of the wheel is very great, it 

 will be cbvious that there ought to be two, three, or 

 more wheels fixed upon the same axle, all of the 

 same diameter, for the purpose of fixing the tloat- 

 boarils, and keeping them firm in every part. 



Wherever water is found to move forward v/irii a 

 progrefsive motion, it descends from a higher to a 

 lower situation, by reason of the prefsureof its own 

 weight always tending towards the lowest place. 

 The greater, therefore, the inclination is «f the sur- 

 face over which it flows, the greater will be its rapi- 

 dity ; and, in proportion to the quantity of water mo- 

 ving forward, will be its strength, when movin^g 

 with the same degree of velocity. 



While water is thus moving, if any object be laid 

 acrofs thestream, it will either stop the current, so as 

 to form a dam, or it will be carried dov/n the 3tr<»n\ 



