342 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 18. 



paradox in hydraulics. But water is supposed to cohere in all its parts. These 

 two corollaries arise from case 1. 



Cor. 15. — From case 2 there is given a method of estimating the motion of 

 the blood in any artery. 



Cor, l6. — Given any two arteries, that transmit an equal mass of blood, the 

 impetus of the blood is greater in the more remote artery from the heart than 

 in the nearer. Which is a paradox in the animal economy worthy observation. 



Cor. 17 — From case 3 there arises another paradox in the animal economy, 

 viz. that the motion or impetus of the blood is greater in all the capillary 

 arteries, taken together, than in the aorta itself. And in like manner it is 

 greater in the capillary veins than in the arteries. 



Cor. 18 — From case 4 is deduced a method of determining the motion of 

 the blood in any vein. 



Cor. IQ. — From the same case is deduced a third paradox in the animal eco- 

 nomy, viz. that the impetus of the blood is greater in any vein than in its cor- 

 responding artery, and consequently that it is greater in the vena cava than in 

 the aorta. 



Problem 1 . — To find the motion of the air, expired from the lungs. 



Let / be = the length of the whole wind-pipe, from the mouth and nostrils 

 to the extreme ramifications of the trachea; q = the quantity of air emitted 

 from the lungs in a mean expiration; a = the quantity of air in the strongest 

 expiration ; t = the time of the mean expiration ; t = the time of the strongest 

 expiration. Then, by theor. 3, case 3, the motion of the air emitted from the 

 lungs, in a mean expiration, is = ^, and in the strongest expiration := — ; that 

 is, the motion of the air, expired from the lungs, is equal to the motion of the 

 bulk of air, emitted in one expiration, whose velocity is such as to run over the 

 length of the whole wind-pipe in the time of expiration, a. e. i. 



Borelli, by an experiment, defined the quantity of air emitted in a mean expi- 

 ration, to be about 18 or 20 cubic inches. But this quantity is different, not 

 only in different persons, but even at different times in one and the same per- 

 son; I made the experiment in the following manner: I appended a weight to 

 the lower part of a moistened bladder, and fitting to its upper part a glass tube 

 about an inch in diameter, and stopping my nostrils, gently inspired air into the 

 bladder, for the space of three seconds of time, the weight in the mean time 

 resting on a table. Afterwards I immersed the bladder, with its included air 

 and appended weight, into water, contained in a cylindrical vessel, carefully 

 marking the height to which the water rose. Then expressing the air out of 

 the bladder, I immersed it a second time with its weight into the water. On 

 which the bulk of water which, poured into the vessel, made up the height 



