ON HYDRAULICS AS A BRANCH OF ENGINEERING. 177 



The time was constantly noticed by an excellent stop-watch, 

 made by Breguet; and the opening of the orifices, the charges 

 of the fluid in the reservoir, as well as the level of the water in 

 the gauge basin relative to each expense of fluid, were always 

 measured to the tenth of a millmietre, so that, even under the 

 most unfavourable circumstances, the approximation was at least 

 to g^odth part of the total result. The total disposable fall or 

 height, counting from the ordinary surface of the Moselle river, 

 was four metres, from which two metres were deducted for the 

 gauge basin, leaving only a fall of two metres under the most 

 favourable circumstances ; and in the subsequent experiments 

 of 1828 the height never exceeded 1-60 metre, sufficiently 

 high for all practical purposes. An apparatus was provided 

 for regulating the height of the orifice and the surface of the 

 water in the reservoirs, and for tracing with the greatest accu- 

 racy the forms and sections of the fluid veins before and after 

 issuing from the orifices, and the depressions experienced by 

 the surface of the water previously to its issuing from an open- 

 ing of twenty centimetres square, the upper side of which was 

 on a level with the surface of the water in the reservoir. These 

 depressions are recorded in the Tables, 



1st, On the expenditure of water through rectangular verti- 

 cal orifices, twenty centimetres square, and varying in height 

 from one to twenty centimetres, under charges of from '0174 

 of a metre to 1*6901 metre: 



2ndly, On the expenditures of water from the similar-sized 

 orifices, open at the top, but under charges of from two to 

 twenty-two centimetres. 



The whole is comprised in eleven Tables of 241 experiments, 

 to which is added a twelfth Table, showing the value of the co- 

 efficients of contraction for complete orifices, from twenty cen- 

 timetres square to one centimetre, calculated according to the 

 following formula: 



D for the height of the orifices, where* 



D = los/^^^l{h-¥) \/2^ ^^i-^ being the theo- 

 retical expense relative to the velocity ; 



or the theoretical expense, having regard to the influence of 

 the orifice. 



• That is, where / = 0'20 metre, heing the horizontal breadth of all the orifices ; 

 h = the charge of the fluid on the lower part of the orifice ; 

 A'=: the charge in the upper or variable side of the orifice ; 

 o = A — V the thickness of the vein of water. 



18.^3. V 



