i72 farmers' and mechanics' journal. 



of cross-bars, or a massy circular rim, be connected with the ma^ 

 chinery, all these inconveniences will be removed. As every Ayr 

 wheel must revolve with great rapidity, the momentum of its cir- 

 cumference must be very considerable, and will consequently re- 

 sist every attempt either to accelerate or retard its motion. When 

 the machine, therefore, has been put in motion, the fly-wheel will 

 be whirling with an uniform celerity, and with a force capable of 

 continuing that celerity when there is any relaxation in the impel- 

 ling power. After a short rest, the animal renews his efforts, but 

 the machine is now moving with its former velocity, and these 

 fresh efforts will have a tendency to increase the velocity ; the fly, 

 however, now acts as a resisting power, receives the greatest part 

 of the superfluous motion, and causes the machinery to preserve 

 its original celerity. In this way the fly secures to the engine an 

 uniform motion, whether the animal takes occasional relaxation, or 

 exerts his force with redoubled ardor. 



" In machines built upon a large scale, there is no necessity for 

 the interposition of a fly, as the inerlia of the machinery supplies 

 its place, and resists every change of motion that may be generated 

 by an unequal admission of the corn. 



" A variation in the velocity of engines arises also from the na- 

 ture of the machinery. Let us suppose that the weight of 1000 

 pounds is to be raised from the bottom of a well fifty ieai deep, by 

 means of a bucket attached to an iron chain which winds round ^ 

 barrel or cylinder ; and that every foot in length of this chajn 

 weighs two pounds : it is evident that the resistance to be over- 

 come in the first moment, is 1000 pounds, added to 50 pounds, the 

 weight of the chain ; and that this resistance diminishes gradually, 

 as the chain coils round the cylinder, till it becomes only 1000 

 pounds, when the chain is completely wound up. The resistance, 

 therefore, decreases from 1050 to 1000 pounds ; and if the impeU 

 ling power is inanimate, the velocity of the bucket will gradually 

 increase ; but if an animal is employed, it wjll generally propor- 

 tion its action to the resisting load, and must therefore pull with a 

 greater or less force, according as the bucket is near the bottom or 

 top of the well. In this case, however, the assistance of a fly may 

 be dispensed with, because the resistance diminishes uniformly, 

 and may be rendered constant, by making the barrel conical, so 

 that the chain may wind upon the part nearest the vertex at the 

 commencement of the motion, the diameter of the barrel gradually 

 increasing as the weight diminishes. In this way the variable re- 

 sistance will be equalized much better than by the application of a 

 fly-wheel ; for the fly, having no power of its own, must necessa- 

 rily waste the impelling power. 



" When machinery is driven by a single stroke steam-engine, 

 there is such an inequality in the impelling power, that, for two or 

 three seconds, it does not act at all. During this interval of inac- 

 tivity, the machinery would necessarily stop, were it not impelled 

 by a massy fly-wheel of a great diameter, revolving with rapidity, 

 till the moving power again resumes its energy. 



