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XIII. Hydraulic Investigations, subservient to an intended Croo- 
nian Lecture on the Motion of the Blood. By Thomas 
Young, M. D. For. Sec. R. S. 
Read May 5, 1808. 
I. Of the Friction and Discharge of Fluids running in Pipes , 
and of the Velocity of Rivers. 
Having lately fixed on the discussion of the nature of in- 
flammation, for the subject of an academical exercise, I found 
it necessary to examine attentively the mechanical principles 
of the circulation of the blood, and to investigate minutely 
and comprehensively the motion of fluids in pipes, as affected 
by friction, the resistance occasioned by flexure, the laws of 
the propagation of an impulse through the fluid contained in 
an elastic tube, the magnitude of a pulsation in different parts 
of a conical vessel, and the effect of a contraction advancing 
progressively through the length of a given canal. The phy- 
siological 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 advisable to communicate, in a 
separate paper, such conclusions, as may be interesting to 
some persons, who do not concern themselves with disqui- 
sitions of a physiological nature ; and I imagine it may be as 
agreeable to the Society that they should be submitted at pre- 
sent to their consideration, as that they should be withheld until 
the time appointed 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 
