152 APPENDIX II. 



" Besides these estimated (and certainly not over- 

 estimated) items, there are several others which 

 cannot be even approximately calculated, but the 

 sum of which, if it could be obtained, would pro- 

 bably exceed even our present large total. We will 

 try to give at least some sort of an account of them. 

 It must first be remembered that in the steepest 

 mountain path there are occasional level portions, or 

 even descents. In traversing such places the 

 muscles of the leg are exerted as they are in ascend- 

 ing, but the whole work performed is transformed 

 back into heat. The same force-producing process, 

 however, must be going on in the muscles as if work 

 were being performed which did not undergo this 

 transformation. In order to make this point yet 

 clearer we may take into consideration that the 

 whole work of the ascent only existed temporarily 

 as work. On the following day the result was re- 

 versed ; our bodies approached the centre of the 

 earth by as much as they had receded from it the 

 day before, and, in consequence, on the second day 

 an amount of heat was liberated equal to the amount 

 of work previously performed. The two parts of 

 the action, which in this case were performed on 

 two separate days, take place in walking on level 

 ground in the space of a footstep. 



" Let us observe, besides, that in an ascent it is 

 not only those muscles of the leg specially devoted 

 to climbing which are exerted ; the arms, head, and 

 trunk are continually in motion. For all these 

 movements force-generating processes are necessary, 

 the result of which cannot, however, figure in our 



