100 MOVEMENT 



happens in the case of jointed pendulums. The alter- 

 nating swing of our lower extremities in running and 

 walking is also of this nature, for while the thigh 

 swings from the hip joint, the leg swings from the 

 knees, and the foot from the ankle. The movements 

 which act and react upon one another produce very 

 complicated results. Fig. 69 shows how chronophoto- 

 graphy can reproduce all the details. 



The Vibration of Flexible Rods. — A distinguished 

 officer in the French army occupied in studying pro- 

 blems in ballistics, was anxious to discover whether 

 the transverse vibrations of the barrel of a gun were 



Fig. 7u. — Vibrations of an elastic and wooden rod. 



transmitted to the extremity of the weapon. He was 

 under the impression that, in vibrations of this kind 

 occurring in flexible rods, they were equally felt along 

 the entire length, and that even in the last segments 

 the vibrations still occurred in the form of curves. 

 The experiment, made by means of chronophotography, 

 showed that this was not the case. Transverse vibra- 

 tions imparted to a rod were represented at the terminal 

 segments as rectilinear discursions (Fig. 70). 



The Rolling of Ships.— The so-called "rolling" of 

 ships presents a very complicated series of- problems, 

 involving, as it does, not only the oscillations of the 

 boat itself, but also the movements imparted to it by 



