WATER. 



at the diftance of about half its diameter from the orifice, 

 from I to .665, according to the mean different ilatements 

 above quoted : hence the diameter is reduced to .815. 



The quantity of water difcharged is very nearly, but not 

 quite, fufEcient to fill this feftion with the velocity due, or 

 correfponding to the height. For finding accurately the 

 quantity difcharged, the area of the orifice muft be fuppofed 

 to be further diminifhed to .619 on account of friftion. 



In regard to the accuracy of this rule, we muft refer to 

 the following table, which contains the refults of 35 experi- 



ments, and alfo the calculation for each. Wc have been 

 obliged to rejeft about 1 2 other experiments, becaufe they 

 would not accord with the theorem ; but in nearly all of 

 them, the velocity was greater than the rule, and thofe 

 which are lefs we have preferved. This was done, becaufe 

 we fufpeft that many of the cafes were not apertures in thin 

 plates ; but in wood planks of confiderable thicknefs, fuch 

 as fluices, the difcharge would then be greater than our 

 rule fuppofes, and fuch cafes (liould be clafled with another 

 defcription of aperture. 



Table of Experiments on the Efflux of Water from Apertures on thin Plates. 



Thefe are the refults of the difcharge through orifices in 

 a thin plate. If we apply to the orifice the fhorteft cylin- 

 drical pipe, that will caufe the ftream to adhere every where 

 to its fides, we fhall find that its length muft be twice its dia- 

 meter. The difcharge through fuch a tube wiU be about 

 4-J.ths of the full quantity, and the velocity may be found 

 by multiolying the full velocities marked in our firft Table 

 by .8125. 



The greateft diminution of velocity is produced by in- 



ferting the pipe fo as to projeft within the infide of the re- 

 fervoir ; probably becaufe of the greater interference of the 

 motions of the particles approaching its orifice in all direc- 

 tions : in this cafe, the velocity is reduced nearly to half of 

 the full velocity. 



It was one great aim of the experiments of Michelotti 

 and Boffut to determine the effefts of contraftion in different 

 cafes. Michelotti, after carefully obferving the form and 

 dimenfions of the natural jet, made various mouth-pieces re- 



fembling 



