WATER. 



fembling it, till he obtained one which produced the fmalleft 

 diminution of the computed difcharge, or till the difcharge 

 computed for the area of its fmaller end approached the 

 neareft to the effedive difcharge. And he at lail obtained 

 one, which gave a difcharge of 983, when the natural dif- 

 charge would have been 1000. This piece was formed by the 

 revolution of a trochoid round the axis of the jet, and the 

 dimenfions were as follow : 



Diameter of the outer orifice = 36 



inner orifice == 46 



Length of the axis = 96 



EyteWein ftates that a conical tube, approaching to the 

 figure of the contraftion of the ftream, procured a difcharge 

 equal to .92 of the full velocity ; and when its edges were 

 rounded off, of .98, calculating on its leaft feftion. 



Venturi has afierted, that the difcharge of a cylindrical 

 pipe may be increafed by the addition of a conical tube at 

 the end of it nearly in the ratio of 5 to 2. (See his experi- 

 ments in our article Discharge. ) But Mr. Eytelwein 

 finds this aflertion fomewhat too ftrong, and obferves, that 



when the pipe is already very long, fcarcely any effeft is pro- 

 duced by the addition of fuch a tube. He made a number of 

 experiments with different pipes, where the ftandard of com- 

 parifon was the time of filling a given veffel out of a large re- 

 ierroir, which was not always kept f nil, becaufe it was difficult 

 to avoid agitation in replenifhing it ; but this circumftance 

 was rendered indifferent to the refults of the experiments by 

 the application of an ingenious theorem. They prove that 

 a compound conical pipe may increafe the difcharge to twice 

 and a half as much as through a fimple orifice, or to more 

 than half as much more as would fill the whole feftion with 

 the velocity due to the height ; but where a confiderable 

 length of pipe intervenes, the additional orifice appears to 

 have little or no effeft. 



The refults of the inveftigations of Boffut, Michelotti, 

 and Eytelwein, agree in a very fatisfaftory manner refpeft- 

 ing the diminution of the difcharge in different cafes ; and 

 we have arranged them in the following Table, which we- 

 recommend to engineers, as affording all the neceffary in- 

 formation to calculate the difcharge from fluices and 

 orifices. 



Vol. XXXVIII. 



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