31 



come more or less completely absorbed in the 

 cross-line, where it has to meet the contrary turn 

 of the opposite cross-Hne end. 



Each point of application will move its end of 

 the cross-line in a direction contrary to its own 

 ooTirse. Thus, the left upper point of application 

 will move its (the right upper end) of the cross-line to 

 the left, by the front, and the right loiver point wiU 

 move its end {the left loiver) to the right, also by tlie 

 front. A new S cannot develop in the cross-hne, 

 but the influence of such an S will spread out 

 from it into the C C of the original curve. 



This new S, arising in the centre of the old one, 

 from the reaction of the cross-line, will be twisted in 

 precisely contrary directions to the latter, and so far 

 as its influence develops, will tend to reverse the 

 original curvatures. In this way each upper end of 

 a cross-line will, as it were, turn up into the C above 

 it, and each lower end down into the G below it — re- 

 versing the curvatures from their positions and car- 

 rying a similar general effect throughout the C. 



This principle, that every set of torsions will, when 

 (Mrried to a certain point, tend to reverse themselves, 

 lies at the foundation of the tlieory of locomotion. 



§ 29. The new curvatures advance, not as the 

 old ones, from the extremities to the centre, but 



