340 ON PHYSICAL DATA 



the results of such investigations, made in the 

 manner described, should be so much at variance 

 with what actually takes place in nature. This 

 circumstance no doubt led Sir John Leslie to 

 remark, " The profound researches of Lagrange 

 and Poisson on the vibrations of fluids, are only- 

 fine speculations, which yet seem to bring out no 

 definite or practical results.'' (See notes to 

 Natural Philosophy.) 



The main points of enquiry in this branch of 

 human knowledge are ; 1st. To determine the 

 amount of resistance of the fluid to the motion of 

 a rigid body of any shape. 2nd. To determine 

 the motion of a rigid mass entirely immersed in 

 two fluids of difiierent specific gravities, each fluid 

 having currents making a given angle with each 

 other. 3rd. To find the velocity with which fluids 

 when subject to a given pressure, issue from the 

 orifice of vessels. 



These questions are among the most important 

 ones in this science, to which our attention and 

 efibrts should be directed. 



In point of utility, the first of these questions 

 is obvious, since the motion, both of rotation and 



