66 



C C ; and, by the second, upon the concaves of the 

 rear convexes, in each S. 



As now the moyement of the socket discharges 

 the first, tJie front C C will be discharged the first, 

 then the rear C C, in each S separately ; and, the 

 appiiis now being on ribs faced in the exactly 

 opposite directions to those on the convexes, the 

 movement will be backward instead of forward. 



The ribs of the concaves, as thus used in retro- 

 gression, will leave and take the ground from the 

 opposite bevels to those from which they would 

 have left and taken it had they been on a convex 

 in progression. 



The convexes, being still the parts primarily 

 affected by the tractions (§ 54), and the appuis, 

 now only changing their bearings with the actual 

 change of the spinal curves (§ 61), the springs of 

 the two C C in each S will be more synchronous in 

 retrogression than in progression. 



§ 71. Third result. The effect of an attempted 

 repetition of any one of the four movements of the 

 ball and socket on the same track, that is not 

 allowing any transformation of one movement into 

 another, wiU be to pass a part of the gathering to 

 the opposite side, or, rather, perhaps, to give back 

 part of the gathering belonging to that point of 



