. The roads and railroads, vehicles, and modes of travelling, of ancient and modern countries; with accounts of bridges, tunnels and canals, in various parts of the world . ,renders it difficult either to set it in motion, or to accele- DETAILS OF STEAM-ENGINE, 289 rate its motion ; and its momentum, wlien once calledforth, renders it equally difficult to arrest or retard itsmotion. These properties give it a remarkably equalizingpower: for, when once fairly set going, it has so great atendency to go on in one uniform state of motion, that allthe little variations and irregularities in the vel
. The roads and railroads, vehicles, and modes of travelling, of ancient and modern countries; with accounts of bridges, tunnels and canals, in various parts of the world . ,renders it difficult either to set it in motion, or to accele- DETAILS OF STEAM-ENGINE, 289 rate its motion ; and its momentum, wlien once calledforth, renders it equally difficult to arrest or retard itsmotion. These properties give it a remarkably equalizingpower: for, when once fairly set going, it has so great atendency to go on in one uniform state of motion, that allthe little variations and irregularities in the velocity ofthe machine, are, as it Avere, absorbed and neutralized, soas to produce no sensible effect. Even were the forma-tion of steam to stop for a short time, the want of thisprime mover would not be felt, because the momentum ofthe fly-wheel would continue to bear it round with appa-rently undiminished velocity. This simple regulator isnot, hoAvever, found sufficient of itself; and there is intro-duced in all stationary engines another contrivance calleda gover?io7\ This consists of an upright axle a b con-nected with some rapidly revolving part of the In the upper part of this axle is a fixed collar, to Avhich arehung by joints the pendulums cc, of which there are twoand sometimes four. These are furnished with balls of brassor iron; which, when the engine is at rest, hang down andtouch the upright axle: but when the axle ab revolves. 290 LOCOMOTIVE STEAM-EXGIXE. they fly out (as represented in the figure) by virtue of theircentrifugal force; and the more rapidly they revolve thegreater becomes this force, and the greater becomes theirdistance from their centre of motion. Each of these armsor pendulums has attached to it at p q, a link or bar ofiron 7K n, and the two or four links all meet in a move-able ring, or collar E, which slides up and dowTi the , when the engine is working too rapidly, the balls •c c fly out, and lift up the collar E above its
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