l£4 Hydraulic Investigations, 



contained in an elastic tube, the magnitude of a pulsation 

 in different parts of a conical vessel, and the effect of a con- 

 traction advancing progressively through the length of a 

 given canal. The? physiological application of the results of 

 these inquiries I shall have the honour of laying before the 

 Royal Society at a future time ; but I have thought it ad- 

 visable to communicate, in a separate paper, such conclu- 

 sions, as may be interesting to some persons, who do not 

 concern themselves with disquisitions of a physiological na- 

 ture; and I imagine it may be as agreeable to the Society 

 that they should be submitted at present to their considera- 

 tion, as that they should be withheld until the time ap- 

 pointed for the delivery of the Croonian Lecture. 



It has been observed by the late Professor Robison, that 

 the comparison of the Chevalier Dubuat's calculations with 

 his experiments is in all respects extremely satisfactory; that 

 it exhibits a beautiful specimen of the means of expressing 

 the general result of an extensive series of observations in an 

 analytical formula, and that it docs honour to the penetra- 

 tion, skill, and address of Mr. Dubuat, and of Mr. de St. 

 Honore, who assisted him in the construction of his ex- 

 pressions. 1 am by no means disposed to dissent from this 

 encomium; and I ai^ree with Professor Robison, and with 

 all other late authors on hydraulics, in applauding the un- 

 usually accurate coincidence between these theorems and the 

 experiments from which thev were deduced. But I have 

 already taken the liberty of remarking, in my lecture on the 

 history of hydraulics, that the form of these expiessions is 

 by no means so convenient for practice as it might have 

 Been rendered; and they are also liable to still greater ob- 

 jections in particular cases, since, when the pipe is cither 

 extremely narrow, or extremely long, they become com- 

 pletely erroneous : for notwithstanding Mr. Dubuat seems 

 to be of opinion, that a canal may have a finite inclination, 

 and yet the water contained in it may remain perfectly at 

 rest, and that no force can be sufficient to make water (low 

 in any finite quantity through a tube less than one twenty- 

 fifth of an inch in diameter; it can scarcely require an ar- 

 gument to showj that he is mistaken in both t[iese respects. 

 2 It 



