394 



FARMERS' REGISTER. 



rNo. 5. 



compression, slip to one side, and if not confi- 

 ned, ihey produce motion. In this thing, water 

 or fluids differ mainly from solid bodies: the latter 

 press only at the bottom, but the former have a 

 lateral pressure in addition: and the nearer they 

 approach the nature of fluids, the more they have 

 of this property. Thus, in a barrel of shot, or 

 sand, there is a pressure on the sides; hence such 

 bodies have been called by philosophers, gross 

 fluids. The pressure itself, which causes the mo- 

 tion here, is produced by the weight of the atmos- 

 phere, and the force of gravitation; but these 

 would not produce motion in a solid body, because 

 they have no lateral pressure. Having started 

 the motion then by pressure, let us see how it is 

 kept up by gravity. Water, like every other bo- 

 dy, is subject to the force of gravitation — (with 

 this difference, that its force on water may be 

 overcome by removing the atmospheric pressure, 

 and making the particles extrertiely light by hear.) 

 By this law, a drop of ram falls to the earth; and if 

 it be caught on the side of a house or inclined plane, 

 it retards its motion some, but it still rolls on, in pro- 

 portion to the elevation of the plane, until the 

 plane be placed perfectly level or horizontal, when 

 the law of gravitation acting perpendicularly to 

 the plane, pins the drop of water to it and it stops. 



If the plane above mentioned then be the least 

 inclined, the motion of the water in the vessel be- 

 gun by pressure, will be kept up by the force of 

 gravitation: and the velocity or swiftness of the 

 water will be in proportion to the inclination of the 

 plane. Hence we infer that the velocity of the 

 water is always in proportion to the inclination of 

 the plane on which it runs. And therefore by in- 

 creasing the inclination of the plane, we augment 

 the velocity of the water. 



The velocity of water therefore depend* upon 

 its pressure, and the force of gravitation, and these 

 depend upon the depth and inclination of the 

 plane. But the depth of the water depends upon 

 the depth of the channel, and the "fall" depends 

 upon the inclination of the plane, therefore the ve- 

 locity of the water is as the depth of the channel, 

 and the fall which it has. By increasmgthe depth 

 of the channel then, and the fid!, we increase the 

 velocity of the current. 



But again the discharge of the quantity of wa- 

 ter on an inclined plane, or in a channel, (which is 

 nothing more than an inclined plane, on which the 

 water is confined from spreading laterally,) is as 

 its velocity, therefore the discharge of water in any 

 given time, is as the depth of the channel and the 

 tail of the bottom. The velocity of water in a 

 pipe, or open channel, is as its shortness, for the 

 longer the tube the more the resistance the water 

 meets with from friction on the sides, &c, hence 

 a short tube will discharge in a given time, (of the 

 same aperture,) more water than a long one, pro- 

 vided the. head of water to be discharged is the 

 same. By shortening the pipe or channel then, 

 we increase the discharge. 



The velocity of water in conduit pipes, or open 

 canals, is in proportion to their straightness. : 'The 

 motion of a fluid is further obstructed by any vio- 

 lent change of celerity or direction. Whether the 

 channel be contracted or enlarged, the change is 

 unavoidably attended by a proportional loss of'im- 

 pulsion. Any sharp flexure of the pipe or con- 

 duit, will occasion a still greater waste of the in- 



citing force."* -The retardation of velocity of wa- 

 ter in canals and pipes by deflections in them, have 

 been accurately calculated, tor angles of every 

 size. Thus, the retardation produced by a right 

 angle, is greater than that produced by an obtuse 

 — and by an acute angle, greater than either. 

 We may infer therefore, that by straightening the 

 channel, the velocity is increased. 



These are some of the causes that accelerate 

 the velocity of water, in pipes and-canals. There 

 are a variety which retard it. First, by accidental 

 obstacles which it meets with in its course, by 

 crookedness of the channel, &c. By its pressure 

 against the bottom, sides of the channel, and at 

 top by the pressure of the atmosphere against 

 which it rubs. This pressure produces a friction, 

 which retards the motion. This friction is greatest 

 in a stream as you approach the sides and bottom; 

 hence on the surface in the middle of the stream, 

 the velocity is always greatest. Adhesion of the 

 particles of the fluid to the sides of the channel, is 

 another obstacle to motion. We may inter then 

 that in proportion as these obstacles are removed, 

 the velocity of the water is increased; and such as 

 cannot be removed, must be overcome by increas- 

 ing the velocity. 



Having proved then, upon the principles of sci- 

 ence, that the motion, of fluids m conduit pipes, 

 and open canals, is produced and continued by 

 hydrostatic pressure, and the force of gravity — 

 and that the velocity of this motion is increased, 

 1st, by the depth of the channel — 2ndly, by the 

 inclination of the bottom (or fall) — Srdly, by 

 shortening the pipe or channel — 4thly, x by renio- 

 ving obstructions — and 5thly, straightening the 

 channel — we will now by way of application of 

 theory to practice, show that all these causes, are 

 in operation to increase the velocity of the current 

 in the canal, A E C, in the figure exhibited above. 



First, it is plain that the new channel is deeper, 

 being cut several feet deeper than the old chan- 

 nel, and more- uniformly so. This is of great ad- 

 vantage in reducing a freshet; for suppose a sheet 

 of water a foot in depth be spread over a flat 144 

 feet in width, and a mile in length, it may be sunk 

 into a ditch 12 by 12 feet deep, leaving out the ve- 

 locity of the water. An enlargement of the ca- 

 pacity of the channel, is of little advantage how- 

 ever, where water is constantly accumulating with- 

 out increased velocity. This capacity in depth 

 and width of the channel is not stationary, but in- 

 creases with the velocity of the stream. 



Secondly. It is plain that the (all or inclination 

 of the bottom of the ditch is increased: for the 

 fall which was before extended alonp;amile and a 

 half; is brought within three-quarters of a mile. 

 This makes the difference in the velocity and dis- 

 charge of water, about the same as between the 

 velocity and discharge of two troughs, one of 

 which is half as long, and double of the elevation 

 of the other (that is doubly as slanting.) 



Thirdly. It is very evident by looking on the 

 figure, the distance, and of course the channel, is 

 shortened. The deserted part of the old channel 

 is nearly, if not quite, double the length of the new 

 channel; hence the pipe through which the water 

 now flows, is shorter than the former one; and 

 therefore the velocity and discharge is greater. 



Fourthly. It is further manifest that the new 



"Dr. Jamieson's Dictionary of Arts, Sciences, &c. 



