67^ 



NA TURE 



[August 15, 1901 



Project the first image of a series (Fig. i) on to a 

 piece of paper, mark the ground Hne and a fixed point on 

 it, ;• — a small stick planted in the ground — then trace 



Fig. 3.— Putting the weight by Sheldon. 



with care the contour of the body and limbs of the 

 gymnast. This done, project the second figure of the 



NO. 1659, VOL. 64] 



series. In order to bring this image into its correct 

 position, relative to the first, shift the paper until the 

 ground line and the point of reference correspond with 



those points 

 already marked 

 on the paper. 

 We shall see 

 that the second 

 image does not 

 coincide with 

 the first ; since 

 each part of the 

 body has moved, 

 trace the outline 

 of the second 

 image and re- 

 peat the opera- 

 tion for each 

 image in the 

 series. The re- 

 sult is a com- 

 posite diagram, 

 and by reference 

 to the original 

 pictures it is 

 easily inter- 

 preted. In the 

 composite dia- 

 gram only every 

 third image in 

 the original has 

 been used, 

 otherwise the 

 result would 

 have been con- 

 fusing. In Figs. 

 I and 3 the 

 movements of 

 the athlete are 

 put before us 

 in series. He 

 begins with a 

 jump, which im- 

 parts a certain 

 acceleration to 

 the shot: during 

 this period the 

 arm is inactive, 

 since the shot 

 rests on the 

 shoulder. Next 

 is added a new 

 ace eleration, 

 due to the arm. 

 In order to dis- 

 cover, for ex- 

 ample, the force 

 acting on the 

 shot at any in- 

 stant, all the 

 images of the 

 shot must be 

 represented (the 

 figure of the 

 man being left 

 out, as it would 

 complicate the 

 diagram). After 

 the successive 

 positions of the 

 shot have been 

 traced on the 

 paper, the accelerations can be determined and their 

 curve traced ; by means of this the work done by the 



