EQUILIBRATION. 511 



tions which the Earth's crust and atmosphere undergo, those 

 which are not due to the still-progressing motion of the 

 Earth's substance towards its centre of gravity, are due to 

 the still-progressing motion of the Sun's substance towards 

 its centre of gravity. Here it is to be remarked, that this 

 continuance of integration in the Earth and in the Sun, is 

 a continuance of that transformation of sensible motion into 

 insensible motion which we have seen ends in equilibration ; 

 and that the arrival in each case at the extreme of integra- 

 tion, is the arrival at a state in which no more sensible mo- 

 tion remains to be transformed into insensible motion a 

 state in which the forces producing integration and the 

 forces opposing integration, have become equal. 



173. Every living body exhibits, in a four-fold form, 

 the process we are tracing out exhibits it from moment to 

 moment in the balancing of mechanical forces ; from hour to 

 hour in the balancing of functions ; from year to year in the 

 changes of state that compensate changes of condition ; and 

 finally in the complete arrest of vital movements at death. 

 Let us consider the facts under these heads. 



The sensible motion constituting each visible action of 

 an organism, is soon brought to a close by some adverse force 

 within or without the organism. When the arm is raised, 

 the motion given to it is antagonized partly by gravity and 

 partly by the internal resistances consequent on structure; 

 and its motion, thus suffering continual deduction, ends 

 when the arm has reached a position at which the forces are 

 equilibrated. The limits of each systole and diastole of the 

 heart, severally show us a momentary equilibrium between 

 muscular strains that produce opposite movements; and each 

 gush of blood requires to be immediately followed by an- 

 other, because the rapid dissipation of its momentum 

 would otherwise soon bring the mass of circulating fluid to 

 a stand. As much in the actions and re-actions going on 

 among the internal organs, as in the mechanical balanc- 



