IMPROVED sr J.RUMSEY. 193 
LEafy practical rules. 
1. Make the arm of the rotatory tube, from the centre 
of motion to the centre of the aperture, of any conveni- 
ent length, not lefs than + of the perpendicular heizht of 
the water’s furface above thefe centres. 
2. Multiply the length of the arm, in feet, by .614, 
and take the fquare root of the produ& for the proper 
time of a revolution in feconds, and adapt the other parts 
of the machinery to this velocity 3 or, 
3 If at the time of a revolution be given, then, multi- 
ply the fquare of this time by 1.63 for the proportional 
length of the arm. 
4. Multiply together the breadth, depth and velocity 
per fecond of the race, and divide the laft product by 8.924 
times the fquare root of the height, for the area of either 
‘aperture. 
5. Multiply the area of either aperture by the height 
‘of the head of water, and the product by 412 (or by go 
‘on common occafions) for the moving force, eftimated at 
the centres of the apertures in pounds avoirdupois. 
6. The power and volicity at the apertures may be eafi- 
ly reduced to any part of the machinery by the common 
rules of mechanics. 
VOL. II. Bb N*, XXIII, 
