While som'e correspondents have written to us stating that heavy fly wheels were positively necessary to prevent backlash and to produce equable motion in flouring mills, Messrs Hatfield amp; Smith, of Cuyahoga Falls, Ohio, inform us by letter, that after several years' experience, they have formed the opinion that " a heavy fly weeel is but a poor remedy for a badly constructed steam engine" They assert that if a steam engine is properly proportioned, with the valve arranged for the work it has to perform, it will run well with a light fly wheel The performances of the mill engine described on page 208 (whereby ten bushels of wheat were ground to each bushel of fuel consumed), they consider good They (H amp; S) have put up an engine of 12inch bore cylinder, 24inch stroke, boiler 26 feet long, 42 inches in diameter, with two 16inch flues, set in brick arch, which turns out sixty barrels of flour in twelve hours running, using thirty bushels of slack or dross coal, which only costs one dollar per tun in that place This mill belongs to Mr Thayer of Akron, Ohio If we allow four bushels of wheat for each barrel of flour made, no less than eight bushels of wheat are ground to each bushel of lack consumed This is doing good work certainly They have also put up quite a number of engines of the same character for other parties, both for grinding grain and sawing wood, in which coal, wood and sawdust are employed for fuel, and with the same satisfaction as to results They gear their engines for the piston to travel at the rate of fire hundred feet per minute ; cut off steam at half stroke, and use a single slide valve