158 THIRD REPORT 1833. 



investigation *. The example of Michelotti gave a fresh sti- 

 mulus to the exertions of the French philosophers, to whom, 

 after the ItaUans, the science owes the greatest obligations. 

 Accordingly, the Abb^ Bossut, a most zealous and enhght- 

 ened cultivator of hydrodynamics, undertook, at the expense 

 of the French Government, a most extensive and accurate se- 

 ries of experiments, which he published in the year 1771, 

 and a more enlarged edition, in two volumes, in the year 

 1786, entitled Traits Theorique et Experimental (THijdro- 

 namique. The first volume treats of the general principles of 

 hydrostatics and hydraulics, including the pressure and equili- 

 brium of non-elastic and elastic fluids against inflexible and 

 flexible vessels ; the thickness of pipes to resist the pressure 

 of stagnant fluids ; the rise of water in barometers and pumps, 

 and the pressure and equilibrivun of floating bodies ; the ge- 

 neral principles of the motions of fluids through orifices of dif- 

 ferent shapes, and their friction and resistance against the 

 orifices ; the oscillations of water in siphons ; the percussion 

 and resistance of fluids against solids ; and machines moved by 

 the action and reaction of water. The second volume gives a 

 great variety of experiments on the motions of water through 

 orifices and pipes and fountains ; their resistances in rectan- 

 gular or curvilinear channels, and against solids moving through 

 them ; and lastly, of the fire- or steam-engine. In the course 

 of these experiments he found that when the water flowed 

 through an orifice in a thin plate, the contraction of the fluid 

 vein diminished the discharge in the ratio of 16 to 10; and when 

 the fluid was discharged through an additional tube, two or 

 three inches in length, the theoretical discharge was diminished 

 only in the ratio of 16 to 13. In examining the effects of fric- 

 tion, Bossut found that small orifices discharged less water in 

 proportion than large ones, on account of friction, and that, as 

 the height of the reservoir augmented, the fluid vein contracted 

 likewise ; and by combining these two circumstances together, 

 he has furnished the means of measuring with precision the 

 quantity of water discharged either from simple orifices or 

 additional tubes, whether the vessels be constantly full, or be 

 allowed to empty themselves. He endeavoured to point out 

 the law by which the diminution of expenditure takes place, 

 according to the increase in the length of the pipe or the num- 

 ber of its bends ; he examined the effect of friction in dimi- 

 nishing the velocity of a stream in rectangular and curvilinear 

 channels ; and showed that in an open canal, with the same 



* Sperimenti Idraulici, 1767 and 1771. 



