122 Professor H. S. Eele-Shaw [March 31, 



you will notice that it uses both its fore and liind legs as the spokes 

 of a wheel on which it rolls when walking (exactly as man does), 

 though it rolls and swings alternately in galloping. The same kind 

 of diagram could be constructed for the effort exerted at different 

 speeds by the horse, as has been produced by Marey for the man, 

 only the distribution of energy would probably be very different. 



Turning next to other animals, it is interesting to observe that a 

 greyhound gets its high speed in proportion to its size owing to the 

 great flexibility of its long body, which enables it to draw its hind 

 legs forward each time for the next bound, and also bound forward 

 both from its fore and hind legs. The other animals in galloping 

 have each the same general kind of movement, although the deer, 

 curiously enough, only bounds from its hind legs, and differs in this 

 respect from the horse ; and also it will be noticed the want of 

 flexibility in the body of an animal may be one of the causes of its 

 relatively slow speed. But whether it be man, horse, dog, or any 

 other animal, the same characteristic is found, namely, that locomo- 

 tion, apart from the bounding action, takes place by a sort of rolling 

 action on the ground. The idea which had persisted since the de- 

 lineation of horses in Assyrian and Egyptian pictures, that both the 

 fore or both the hind legs are put on the ground simultaneously, 

 is thus exploded. As Mr. Muy bridge truly said : " When during a 

 gallop, the fore and hind legs are severally and consecutively thrust 

 forwards and backwards to their fullest extent, their comparative 

 inaction may create in the mind of the careless observer an impres- 

 sion of indistinct outlines ; these successive appearances were prob- 

 ably combined by the earliest sculptors and painters, and with gro- 

 tesque exaggeration adopted as the solitary position to illustrate great 

 speed." As a matter of fact, each leg in turn, as it rests on the 

 ground, stops for a moment just as much as in the forward position 

 above mentioned, and if you watch a dog galloping you can see 

 quite clearly the rolling stroke action I have mentioned. 



With the above facts in mind, we can understand exactly the 

 limitations to animal locomotion. In the words of Mr. Muybridge : 

 " When the body of an animal is being carried forward with uniform 

 motion, the limbs in their relation to it have alternately a progressive 

 and a retrogressive action, their various portions accelerating in com- 

 parative speed and repose as they extend downwards to tlie feet, 

 which are subjected to successive changes from a condition of abso- 

 lute rest, to a varying increased velocity in comparison with that of 

 the body." Hence, all animal locomotion absolutely lacks that con- 

 tinuity of movement, the production of which we shall see is the dis- 

 tinguishing feature and the direct cause of the high speeds attained 

 in mechanical locomotion. 



The exchange of the intermittent movement of nature for one 

 having the desired continuity of movement has been effected by means 

 of what is possibly the greatest and yet the simplest of all human 



