History of the Science of Hydraulics. 197 



have placed him in the foremost rank of writers on this sub- 

 ject. He shows in his third volume, by discussing experi- 

 ments, that the resistances of fluids in uniform motion may 

 be represented, as indicated by Coulomb, by an expression in- 

 volving only two terms, one containing the first, and the other 

 the second, power of the mean velocity ; but that these terras 

 should be affected by independent coefficients, and not by a 

 common one, as advocated by Coulomb and Girard. He then 

 deduces the value of these coefiicients for pipes and canals by 

 employing two methods given by La Place in his Mecanique 

 Celeste, and by a general equalization of disturbing causes; 

 he gives a new formula of his own for obtaining the mean 

 velocity, etc., from that of the surface. 



He published an additional paper in 1825, giving methods 

 of simplifying the application of his formulaj. In 180i, Le- 

 creulx published his Recherches sur la Formation et I'Exist- 

 ence des E,uisseaux, Rivieres et 'J^orrents. 



In 1808-9 appeared the work of Funk, a celebrated Ger- 

 man scientist, upon hydraulic architecture. M. Krayenhoflf 

 published in 1885, his "Recuil des Observations Hydrauli- 

 ques et Topographiques faites en Hollande," containing a full 

 collection of tables of observations upon the hydrography and 

 topography of Holland, a standard work of great value. He 

 made detailed measurements of discharge, slope of surface, 

 etc., determining the velocity by means of observing the time 

 of transit past a base line of vertical poles reaching from the 

 surface nearly to the bottom. In the Memoirs of the Acad- 

 emy of Berlin, 1814, 1815, appeared the celebrated articles of 

 M. Eytelwein, giving new values to the constants in de Bouy's 

 formulas, etc. In 1816, Girard read before the French Acad- 

 emy his valuable work upon the Nile ; his graphic representa- 

 tion of the daily gauges kept for the years 1799, 1800 and 

 1801, is the first diagram of the kind on record. In 1820 

 appeared Funk's second work on hydraulics. Escherde la 

 Linth, in 1821, read a paper before the Helvetic Society of 



