summary of hydraulics. 81 



the motion muft be equal to the force that generates it ; that 



is, to the weight of the column of water operating during the 



time neceffary for its acquiring the given velocity : and the 



quantity of water arriving during this time, being equal to 



twice the column of which the length is the height due to the 



velocity, the hydraulic preffure muft be twice the weight of 



fuch a column* The relative impulfe againft a plane in mo-or when the 



tion, muft be determined from the difference of the velocities *.P lane recedc9 * 



but when all the water of a ftream ftrikes againft a plane, the 



effect of the impulfe may be more fimply determined, as if a 



folid body ftruck the plane with the relative velocity ; and this 



is nearly what happens in underftiot water-wheels. 



When a detached jet ft rikes againft a plane, it appears, Detached jet, 

 from the experiments of Boffut and Langfdorf, that its effect 

 is equal to the weight of an equal column of twice the height 

 due to the velocity ; but the plane muft be at leaft four times 

 as large in diameter as the jet; if it be only of the fame fize, 

 the effect will be but one half as great. In an unlimited Unlimited 

 ftream,- the impulfe is alfo nearly determined from the height ream > 

 correfponding to the velocity ; and it appears, that the effect 

 is nearly doubled by confining the ftream to prevent its divert- confined in a 

 ing laterally from the float-boards. Channel. 



For oblique furfaces, the effect of a detached jet in its own Oblique furfaces 

 direction, appears to vary as the fquare of the fine of the angle °PP ofed t0 a J et> 

 of incidence; but, for motions in open water, we muft add to 

 this fquare about -J of the difference of the fine from the radius: 

 a correction which is tolerably accurate, until the inclination 

 becomes very great. Mr. Eytelwein found the refiftance to 

 the motion of a fphere nearly |- of the refiftance to a circle 

 equal to its fection : perhaps it was a hemifphere, otherwife it 

 is difficult to reconcile the refult with other experiments in 

 Which it has appeared to be only ~. 



Mr. Eytelwein informs us, that at the temperature 14° of Weight of diftiU 

 Reaumur, or 62>\ of Fahrenheit, a cubic foot of diftilled water led waMr * 

 weighs 66.0656 pounds of Cologne, or 65.9368 commercial 

 pounds of Berlin. According to Sir George Shuckburgh's 

 experiment, an Englifh cubic foot of diftilled water at 66° 

 weighs 997 ounces avoirdupois ; and water expands for every 



I degree .000165 : hence the pound of Cologne is 1.0312 Eng- 

 lifh avoirdupois pounds, and that of Berlin 1.0332. 

 Chapter 12. Of overlhot water-wheels. Overihotwhetlgj 



The power which operates upon overlhot wheels, is divided 

 Vol. III.— October, 1802. G into 



