634 ANNUAL, KEPORT SMITHSONIAN INSTITUTION, 1911. 



structed 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 

 delineation 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 

 forward and backward to their fullest extent, their comparative inaction may create 

 in the mind of the careless observer an impression of indistinct outlines; these suc- 

 cessive appearances were probably combined by the earliest sculptors and painters, 

 and with grotesque 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 comparative speed and repose as they extend 

 downward to the feet, which are subjected to successive changes from a condition 

 of absolute rest to a varying increased velocity in comparison with that of the body. 



Hence, all animal locomotion absolutely lacks that continuity of 

 movement, the production of which we shall see is the distinguishing 

 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 

 inventions, namely, the wheel. The wheel was made and used prob- 

 ably thousands of years before man learned to replace muscular effort 



