352 NATURAL THEOLOGY. 



the tube ; and the ajutage must rise from the hori- 

 zontal pipe with a gentle sweep, or the jet wilS 

 not reach so high as it ought to do, from cal- 

 culating the height of the water in the reservoir. 

 This circumstance explains the parabolic curve 

 which the great artery takes in going off from the 

 heart ; it explains also why the branches of this 

 great artery go off at different angles, and why 

 near the heart the branch goes off at a greater 

 angle from the direction of the stream.* 



We have, perhaps, said enough to remove the 

 notion, that there is any thing like irregularity in 

 the course and distribution of the vessels of the 

 living body. But there are some other laws of 

 hydraulics which give interest lo the sti ueiure and 

 action of the circulating vessels. The elasticity 

 of the coats of the artery is a subject of irnport- 

 ance in surgical pathology, and has very properly 

 been deeply considered. This power has not, 

 however, met with sufficient attention as one of 

 the forces propelling the blood. 



The law of inertia is easily comprehended as it 

 regards solids. Every thing about us proves that 

 it is more difficult to move a body at rest, than to 

 accelerate it when it has been put in motion. 

 The same law holds of a column of water in a 

 pipe : it is easier to keep it in motion than to put 

 it in motion from a state of rest. From this it 

 follows, that in propelling water through a pipe 



* This refers more especially to the intercostal arteries. 



