128 NOTES TO BOOK VI. 



(c.) p. 72. The Hydrodynamical problems referred 

 to in the text are, the laws of a fluid issuing from a vessel, 

 the laws of the motion of water in pipes, canals, and 

 rivers, and the laws of the resistance of fluids. To these 

 may be added, as an hydrodynamical problem important 

 in theory, in experiment, and in the comparison of the two, 

 the laws of waves. Newton gave, in the Principia, an ex- 

 planation of the waves of water (Lib. u. Prop. 44,) which 

 appears to proceed upon an erroneous view of the nature 

 of the motion of the fluid : but in his solution of the pro- 

 blem of sound, appeared, for the first time, a correct view 

 of the propagation of an undulation in a fluid. The his- 

 tory of this subject, as bearing upon the theory of sound, 

 is given in Book vni. : but I may here remark, that the 

 laws of the motion of waves have been pursued experi- 

 mentally by various persons, as Bremontier (RecJierckes sur 

 le Mouvement des Ondes, 1809), Emy (Du Mouvement des 

 Ondes, 1831), the Webers (Wettenlehre, 1825); and by 

 Mr. Scott Russell (Reports of the British Association, 

 1844). The analytical theory has been carried on by 

 Poisson, Cauchy, and, among ourselves, by Prof. Kelland 

 (Edin. Trans.) , and Mr. Airy (in the article Tides, in the 

 Encyclopaedia Metropolitana). And though theory and 

 experiment have not yet been brought into complete 

 accordance, great progress has been made in that work, 

 and the remaining chasm between the two is manifestly 

 due only to the incompleteness of both. 



(D.) p. 107. In the first edition of this History, I had 

 ascribed to Lagrange the invention of the Method of 

 Variation of Elements in the theory of Perturbations. 

 But justice to Euler requires that we should assign this 

 distinction to him ; at least, next to Newton, whose mode. 



