102 Mr. J. Aitken on some Experiments on 



links alters the form of the curves ; A shows how the flatten- 

 ing is produced at the entrance to the curves. Suppose the 

 link 1 to be moving in a straight path and just entering on 

 the curve c d, the links 2, 3, &c. have entered the curve. The 

 sketch shows the position of the links with regard to the line 

 of tension. The links tend to keep their centre line vertical, 

 and resist moving in the curved line cd. The sketch also 

 shows that, by doing so, in passing round the curve the ten- 

 sion on each end of the link is no longer in a straight line, 

 but acts as a " couple," tending to cause the link to rotate. 

 Again, B shows the effect of the rotation of the links when 

 passing from a curved into a straight path; the link 1 is 

 moving in the curved path c d. The outer parts of the links 

 are in this case moving quicker than the inner, the result 

 of which is to throw the centre line of the link inwards, 

 thus causing the link to move inwards, and also forcing the 

 link in front inwards, so causing the links to continue to move 

 in their curved course. This rotation of the links causes the 

 tension in the chain to act as a "couple" on the links as 

 shown, but this time in the opposite direction to the case A, 

 and tends to destroy the rotation. But before the rotation is 

 destroyed, the chain has curved far past its position of rest ; 

 the links have therefore to come back again, and in doing so 

 have a rotation in the opposite direction given them, which 

 again causes them to overshoot the mark, from which they 

 have to be brought back ; and thus, by a continued series of 

 rotations in one direction and then in the other, the well- 

 marked waves shown in the figure are produced. 



We may, by altering the shape of the links, get still more 

 marked effects — if, for instance, instead of placing the pieces 

 of wood on both sides of the tape we place the same size of 

 link all on one side, so that the whole weight of the links shall 

 be on the one side of the line of tension. This form of chain, 

 however, is not so steady in its motion as the other one. If, 

 for instance, we place the tape, that is the line of tension, on 

 the outside of the curve, then the form becomes extremely 

 unsteady. If the two sides of the chain do not take exactly 

 the same curvature, the side with the most curvature tends to 

 turn round the other one, and the chain, if its construction 

 admits of it, turns itself inside out, so placing the line of ten- 

 sion inside the loop. 



X. The length of the links has also an influence on the cur- 

 vature which the chain will assume when in motion. If we 

 make two chains of exactly the same size and kind of wire, so 

 that they shall be exactly alike in every respect except the 

 length of links, when these two chains are hung over the 



