REPORT OX HYDRAULICS. — PART II. 447 



The sixth and last volume, contains the experiments and con- 

 clusions of Bonati in opposition to those of Gennet^, on the 

 Methods of Measuring the Expenditure of Rivers and of Canals 

 of Irrigation adopted by the different provinces of Italy ; and in 

 which the author, after showing the discrepancies which exist 

 between them, gives the preference to the Milanese method. 



A paper by Morri, on the Navigation of Faenza, and some 

 unsatisfactory experiments on the inclination, velocity, and pro- 

 duct of the river Po, together with several observations of minor 

 importance on the rivers Reno, Tiber, Brenta, and Velino, con- 

 clude the new collection. Such may be considered to be the 

 present state of hydraulic science in Italy. In rendering an 

 account of its progress it is impossible to withhold the just 

 tribute which is due to the Italians, namely, that of having been 

 the first to establish hydraulic science upon anything like true 

 principles. 



Progress and Present State of Hydraulics in France, 

 Germany, and England. 



The writers included under the above title may be considered 

 to consist of two classes, viz. theoretical and practical. 



The first have confined themselves to a purely speculative con- 

 sideration of the subject, in extending the chain of geometrical 

 truths without contributing anything to the real progress of 

 the science. 



The last have endeavoured by observation and experiment to 

 arrive at practical inferences. 



Mariotte belongs more properly to the latter class. His 

 treatise on the motion of water, accompanied by an immense 

 number of experiments, in the year 1728, has greatly contri- 

 buted to perfect the science. 



Pitot demonstrated, that in open channels friction diminished 

 in proportion to the diminution of the surfaces in the inverse 

 ratio of the homologous sides ; and that the friction of water 

 moving in tubes at equal velocities, in relation to the volume of 

 water, is in the inverse ratio of the diameters. 



Couplet illustrated this principle very clearly in his experi- 

 ments, although his deductions from them were incorrect. 



Varignon contented himself with reducing the opinions of 

 Guglielmini to geometrical forms. 



Belidor followed the steps of Guglielmini in his great work 

 on Hydraulic Architecture. 



Bossut was the first to follow the steps of the Italian school 

 by combining theoretical with. experimental investigation. His 



