ON THE FUNCTIONS OF THE HEART AND ARTERIES. §7 



with which the blood was forced through the artery, was 



nearly o.e eighth of he whole force of tension, as it appears 



in the former calculation. 



The magnitude of the pulse must diminish in the smaller Diminution of 



arteries in the subduplicate proportion of the increase of \^^ P"'''^ '" 



, ^ 1 ■ n *^^ smaller ar« 



the joint areas, la the same manner a^ the intensity of sound teries. 



is shown to decrease in diverging from a centre, in the sub- 

 duplicate ratio of the quantity of matter affected by its mo- 

 tion at the same time. For example, in the arteries of the 

 tenth order, of which the diameter is one thirteenth of au 

 inch, its magnitude must be only one third as great as in 

 the aorta, that is, the gre-^test progressive velocity of the 

 blood must be eight inches and a half in a second only, and 

 the dilatation one fiftieth part only of the diameter. In the 

 vessels of the twentieth order, the dilatation does not ex- 

 ceed i-TTTT of the diameter, which is itself the 140th part 

 only of ira inch : so that it is not surprising, that Haller 

 shouid have been unable to discover any dilatation in ves- 

 sels of these dimensions, even with the assistance of a pow- 

 erful microscope. If we estimated the magnitude of the 

 pulse in the aorta, from the excess of the temporary above 

 the mean velocity, which would perhaps be justifiable, that 

 magnitude would be still less considerable. 



These calculations agree extremely v/ell with each other, Velocity of 

 and with expeiiment, as far as they relate to the power of '^'"''^ P"'^° ^" 



'^ _ ■' '^ the larger ar- 



the heart, and the affections of the smaller arteries. But teiies more 



there is reason to thnik, that the velocity of the pulse in ^^'"^i,^'^'^^'® 



: , ■ than here 



the larger vessls is much more considerable, than has been stated. 



here stated; and their dilatation is also less conspicuous, 

 when they are exposed to view, than it would probably be, 

 if it were as great as is inferred from the velocity here as- 

 signed. 1 have demonstrated ih the hydraulic investigations 

 which I lately laid before the Rqyal Society, that the velo- 

 city of an impulse passing through a tube, consisting of 

 perfectly elastic materials, is half as great as that of a body 

 supposed to have fallen from the given point to the base 

 of the modular column of the tube ; and that the height of 

 this column is such, that the tube would be extended with- 

 out limit by.its pressure : consequently it must be greater 

 than the height of a column equivalent to the pressure 

 F 2 by 



