The following article presenting the modus operandi for calculating the power of the Parker Water Wheel, is from J. Sloan Esq., of Sloan's Mills, of Floydsburgh. Shelby Co., Ky., who since we referred to his correct and extended information on this subject, on page 336, Vol. 6, Scientific American, has had many letters sent to him for information. This, it is hoped, will give all the knowledge required by future inquirers. " My manner of computing the power of the Parker wheel is as follows, fora wheel of 150 square inches area of issues, and 3 feet diameter, under 9 feet fall, viz., 9X64=576 ; 24 X 150=3600 -H144 =25 X62 -5=1562'5X9= 14062'5 actual power of the water in pounds, theoretically with the assumption ; the discharge is through a fair common aperture in the atmosphere. Diameter ot wheel in feet X3-1416—94248, then 24X60=1440—9-4248 =152-89 revolutions of the wheel per minute provided the velocity of the wheel is the same as the water. The result of repeated experiments I have made, proves the helical sluice of the Parker wheel, retards the water as 33 is to 30-75, which must be deducted; thus, 33 : 30'75 : : 23 : 23'295 cubic feet per second the practical or real discharge of the helical sluice without the wheel. I also found the wheel retarded the water in the sluice as 30 75 is to 25-5; hence we have 30 75 : 255 : : 2%' 295 : 19-3145 cubic feet, the real discharge through the wheel measured in the tale race, on the prineile laid down by Du Bauts lor measuring running water. I found it safe to allow the wheel's periphery to move 7 per cent Jaster than the velocity of the water, a practice of 20 years' standing. The Franklin Institute, in their report, 11th June, 1846, assert that a Parker wheel, under a fall of 1010 feet, made 166 revolutions per minute, and the mechanical effect was 71 per cent., with 1110 cubic feet of water per minute; 101 X64=6464; 25'424X60-1525-44 the theoretical velocity of the water per minute. The diameter of wheel, 36 5 X 31416= 114-668-12=9-55 feet, the circumference of the wheel. Velocity of water 1525-44-9-55 = 159 73 number of revolutions of the wheel per minute, provided the velocity of both were in unison. The wheel made 166—159-73= 627 revolutions of the wheel more than the velocity of the water theoretically. The area of inlet and issue of the wheel was 150 square inches+1525-44=229816-H44=1595-944 cubic Teet per minute theoretically, 685944 cubic feet per minute more than the actual quantity."