542 THE MECHANICAL FUNCTIONS. 



an equal time. Strictly speaking, indeed, it is 

 impossible for even the strongest man to remain 

 on his legs, in precisely the same position, for 

 any considerable length of time. The muscles in 

 action soon become fatigued, and require to be 

 relieved by varying the points of support, so as to 

 bring other muscles into play. Hence the weight 

 of the body is transferred alternately from one foot 

 to the other. The action of standing consists in 

 fact, of a series of small and imperceptible mo- 

 tions, by which the centre of gravity is perpe- 

 tually shifted from one part of the base to ano- 

 ther ; the tendency to fall to any one side being 

 quickly counteracted by an insensible movement 

 in a contrary direction. Long habit has rendered 

 us unconscious of these exertions, which we are, 

 nevertheless, continually making ; but a child 

 learning to walk finds it difficult to accomplish 

 them successfully. It is one among those arts 

 which he has to acquire, and which costs him in 

 the apprenticeship many painful efforts, and 

 many discouraging falls. But whenever nature 

 is the teacher, the scholar makes rapid progress 

 in learning ; and no sooner have the muscles 

 acquired the necessary strength, than the child 

 becomes an adept in balancing its body in various 

 attitudes, and in a very short time is uncon- 

 scious that these actions require exertion. 



In walking, the first effort that is made consists 

 in transferring the whole weight of the body 



