1011] on Travelling at Hiuh Speeds on Surface of Earth. Ill) 



resistance of the atmosphere. Neither is it due to the effective work 

 done in movement, since with a body moving along a level plain, i.e. 

 at a constant distance from the earth's centre, this effective work is 

 nil. To understand the matter we must study the nature of animal 

 loconiocion. The surface of the earth is rough, sliding along it 

 being obviously out of the question ; nature has made provision for 

 animal movement as follows : — one part of the body first rests on 

 the ground, another part supported by this is advanced, being raised 

 clear of the ground, to rest in turn upon the ground and serve in 

 turn as a support, so that the part behind may be raised and advanced 

 to a fresh position. In man and other animals the feet form the 

 points of support for this process ; but the same method of locomo- 

 tion is employed by creatures without feet, which have to crawl or 

 glide, such as snakes or worms. 



This process, whether with animals or reptiles, as you will see, 

 involves in the raising of the body an expenditure of work which is 

 not recovered, and further an expenditure of work in stopping and 

 starting some portion of the body in its movements. My assistant 

 now walks in front of the blackboard holding a piece of chalk 

 level with his head, and you will see the rising and falling motion. 

 I have prepared a wooden model to represent the action of his legs, 

 and you will see that these legs, being equal to his in length, produce 

 almost exactly the same curve underneath, so that you have a com- 

 plete explanation of this movement, viz. the rotation of the hip 

 about the ankle as a pivot. There is a third case of loss, namely, 

 the energy involved in swinging the legs. About thirty years ago 

 the distinguished French professor, Marey, actually investigated the 

 loss involved from each of these three causes, and I have on the wall 

 a diagram in which you will see all three given graphically. The 

 number of steps per minute, you will notice, increases until a pace is 

 reaclietl when it becomes painful to walk faster, and you will also 

 notice from the diagram that at about ninety steps per minute the 

 gait changes to a run, that is to say, a springing action takes place, 

 the hind foot leaving the ground before the front is put down upon it. 



I have another diagram showing how the length of stride at first 

 increases with the pace, and afterwards begins to fall off before the 

 walking breaks into a run. The reason why a man or an animal 

 changes his pace at this point is obvious, and it is because a faster 

 speed is possible with a less effort. As the speed of running is 

 increased the total effort becomes greater, but the three elements 

 shown on the diagram are differently divided ; the rise and fall 

 element is less, but the work done in swinging the legs is more, 

 while the chief element, in the muscular effort expended, is the loss 

 of energy involved in stopping and starting as each spring reaches a 

 maximum. Time does not permit me to pursue this interesting 

 subject further except to point out that exactly similar causes operate 

 in the natural locomotion of other animals which move on legs. 



