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impelled ; and it is well known, that a threshing-machine ne-ver acts with sufficient efficacy, unless when the switchers orbeaters of the drum are moved with considerable velocity. Ithas been ascertained by long experience, that the minimumof this velocity for clean threshing, is 2000 feet per minute;but a velocity of from 2500 to 3000 feet in the minute, ismuch preferable. Where coals are abundant and cheap, thepower of steam may be advantageously substituted for work-ing the threshing-machine, in situations where water cannotbe procured for the purpose, and where windmills are ineligi-ble; and this power has actually been had recourse to in se-veral instances, and it is said with satisfactory results. In everyinstance where water can be procured in sufficient quantity,and at a moderate expence, that is unquestionably the bestand cheapest, and most manageable moving power, and isequally well calculated for threshing-machines of the greatestrequired force, and even for the smallest. Wind is the nextbest for large arable farms; but both it and steam are quiteineligible for small or even moderate sized farms, owing tothe great original expcnce which both require. In small ormoderate sized farms, where water cannot be readily andcheaply procured, horses must be substituted, or oxen may beused with much advantage.
The only objection to the use of water, as the moving powerof the threshing-machine, is, that it may be locked up fromuse during long continued frosts, at a time when litter andfodder are indispensably necessary, and that it is often defi-cient during the long droughts of summer and autumn. Butwhere water can be had in sufficient abundance and constantsupply, though certainly the most manageable and most eco-nomical power that can possibly be used, yet if the supplyis deficient, the addition of a horse power is desirable. Windis often deficient during harvest, and in hard frosts, whenstraw must be procured for thatch, litter, or fodder. On theseaccounts, when it is the moving power, it is necessary thatthe threshing-machine should be provided with a horse-wheel,