ON HYDRAULICS AS A BRANCH OF ENGINEERING. 157 



flowing from orifices in vessels, and through pipes of constant 

 or variable diameters. " But it is greatly to be regretted," 

 says M. Prony, " that Euler had not treated of friction and 

 cohesion, as his theory of the linear motion of air would have 

 applied to the motions of fluids through pipes and conduits, 

 had he not always reasoned on the hypotheses of mathematical 

 fluidity, independently of the resistances which modify it." 



In the year 1765 a very complete work was published at 

 Milan by PauJ Lecchi, a celebrated Milanese engineer, entitled 

 Idrostatica esaminata ne suoi Principi e Stabilite nelle suoi 

 Regole delta Mensura delta Aeque correnti, containing a com- 

 plete examination of all the different theories which had been 

 proposed to explain the phgenomena of effluent water, and the 

 doctrine of the resistance of fluids. The author treats of the 

 velocity and quantity of water, whether absolutely or relatively, 

 which issues from orifices in vessels and reservoirs, according 

 to their different altitudes, and inquires how far the law applies 

 to masses of water flowing in canals and rivers, the velocities 

 and quantities of which he gives the methods of measuring. 

 The extensive and successful practice of Lecchi as an engineer 

 added much to the reputation of his work*. 



In the year 1764 Professor Michelotti of Turin undertook, 

 at the expense of the King of Sardinia, a very extensive series 

 of experiments on running water issuing through orifices and 

 additional tubes placed at different heights in a tower of the 

 finest masonry, twenty feet in height and three feet square 

 inside. The water was supplied by a channel two feet in width, 

 and under pressures of from five to twenty-two feet. The 

 effluent waters were conveyed into a reservoir of ample area, 

 by canals of brick-work lined with stucco, and having various 

 forms and declivities ; and the experiments, particularly on the 

 efilux of water through differently shaped orifices, and addi- 

 tional tubes of different lengths, were most numerous and 

 accurate, and Michelotti was the first who gave representations 

 of the changes which take place in the figure of the fluid vein, 

 after it has issued from the orifice. His expei'iments on the 

 velocities of rivers, by means of the bent tube of Pitot, and by 

 an instrument resembling a water-wheel, called the stadera 

 idraulica, are numerous and interesting ; but, unfortunately, 

 their reduction is complicated with such various circumstances 

 that it is difficult to deinve from them any satisfactoi'y conclu- 

 sions. But Michelotti is justly entitled to the merit of having 

 made the greatest revolution in the science by experimental 



* Sec also Memorie Idrostatico-storiclie, 1773. 



