HYDRAULICS AND ITS APPLICATIONS 



in motion in pipes and open channels, but we have no record that 

 this knoNvh <lge was based on any quantitative laws. 



A treatise by Stevinus, written about 1585, would appear to follow 

 hiMork-ally that of Archimedes. In this the method of obtaining the 

 pressure of a liquid on the sides and base of a containing vessel was first 



demonstrated. 



(.alilro, in a treatise published in 1612, discussed the Hydrostatic 

 Paradox and also the flotation of bodies in water. 



Shortly afterwards Torricelli made an important investigation into the 

 behaviour of a jet when issuing vertically from an orifice, while, since the 

 middle of the seventeenth century, numerous investigators have been at 

 \\ork deducing by experimental observation and theoretical reasoning the 

 laws governing the various manners of motion of liquids, and applying 

 these laws to the development of the science of Hydraulics. Of these 

 i \pcrimentalists perhaps Mariotte, Bernoulli, and D'Alembert, with 

 Poiseuille, Darcy, and Bazin in France ; Bankine, Froude, Osborne 

 Beynolds and James Thomson in England ; Eytelwein, Weisbach, and 

 Hagen in Germany ; Venturi in Italy, with Francis and Hamilton Smith 

 in America, are most worthy of note. 



In spite, however, of all the work which has been so ably accomplished 

 by these and other observers, Hydraulics cannot yet be classed as an exact 

 science. The laws governing many of its phenomena are still imperfectly 

 understood, and the difficulties chiefly analytical to be overcome before 

 all the disturbing factors can be taken fully into account are very great. 

 In such cases, experience, based on the results of experiment, forms the 

 only safe guide. In other cases, however, the deductions of theory 

 are found to be perfectly in accord with observed phenomena, and an 

 attempt will be made in the course of this work to indicate to what extent 

 our knowledge of the forces, controlling any phenomenon is sufficiently 

 accurate and comprehensive to enable theory to be an exact guide, and 

 where, on the other hand, theory, based on insufficient data, is only useful 

 as indicating in what direction a true solution is to be found. 



ART. 2. PHYSICAL PROPERTIES OF WATER. 



In its pure state, water is an almost colourless, transparent, odourless 



liquid, and one of the best solvents to be found in Nature. Its maximum 



ty occurs at 4 C., or 891 F., and under atmospheric pressure it 



freezes at 82 F. and boils at 212 F. The freezing point is lowered, and 



the boiling point raised by an increase in pressure, the opposite being true 



