27 



land as there will be two sucli lines, the one pro- 

 duced by the antagonism of the left upper and right 

 lower forces — the other by that of the right upper 

 and left lower, we shall discriminate the cross-lines 

 as left-riglit and right-left respectively. We shall 

 also name that end of either cross-line on which 

 an upper force draws the upper end, and that on 

 which a lower force draws the lower end, 



§ 21. It is particularly to be observed that the 

 curvature under any point of pressure is always con- 

 cave. 



§ 22. Straightening the rod again, let the point 

 at which the upper diagonal pressure is applied 

 (according to our standard example the left upper) 

 be placed at the front centre of its plane, and then 

 moved in rotation horizontally, the pressure con- 

 tinuing, and let the lower end of the rod be pre- 

 vented from following the movement so that it 

 offers merely a passive resistance to it. There will 

 then be a constantly increasing pressure exerted 

 below the moving point by the reaction through 

 the stretched linear elements of the rod. 



The direct effects of the traction will be in a wind- 

 ing line passing from the point of apphcation, by 

 the front, half way around the rod, to the point 

 where it meets the resistance from the stationary 



