1 66 Life and Matter [chap. ix. 



if it could it would be a straightforward 

 mechanical agent but it can utilise the 

 mechanical properties both of rail and of 

 engine ; it arranged for the rail to be placed 

 in position so that the lateral force thereby 

 exerted should guide all future trains to a 

 desired destination, and it further took steps 

 to design and compose locomotives of 

 sufficient power, and to start them at a 

 prearranged time. It " employs " mechanical 

 stress, as a capitalist employs a labourer, not 

 doing anything itself, but directing the 

 operations. It is impossible to explain 

 all this fully by the laws of mechanics 

 alone, that is to say, no mechanical analysis 

 can be complete and all-embracing, though 

 the whole procedure is fully subject to 

 those laws. 



stress, like that exerted by a pillar or a watershed does no 

 work, and "generates" or transfers no energy; yet the 

 one sustains a roof which would otherwise fall, thereby 

 screening a portion of ground from vegetation; while the 

 other deflects a rain-drop into the Danube or the Rhine. 

 This latter is the kind of force which constrains a stone to 

 revolve in a circle instead of a straight line; a force like 

 that of a groove or slot or channel or " guide." 



