630 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



Seward in 1847, or 64 years ago, still stands. In fact, a study of all 

 the records of 25 distances shows that several of them remain un- 

 broken after comparatively long periods, viz, from a quarter to half 

 a century. 



Thus, so far as his own unaided powers of locomotion are con- 

 cerned, man may be considered, for all practical purposes, to have 

 reached long ago the limit of speed possibility. From earliest times, 

 however, he has brought the muscular effort of other animals into 

 his service, and has devoted his intellect toward improving their 

 speed for his own uses. You will see graphically recorded in figure 1 

 the speeds of all the Derby winners from the year 1856 — i. e.,for more 

 than half a century. The average speed, which may be taken as 

 somewhere above 30 miles an hour, has doubtless slightly increased, 



fEAR 

 Fig. 1.— Derby winners for 55 years. 



but it will be seen from the dotted line which has been drawn at the 

 top of the maximum speeds what comparatively little increase has 

 been obtained for an expenditure of the many millions represented 

 directly and indirectly in the training and breeding of these horses, 

 and it may be reasonably assumed that here again the limit has been 

 reached for the fleetest animal, by the aid of which man can increase 

 his speed of locomotion by using muscular power other than his own. 

 What, then, are the physical reasons for this limitation? It is 

 not due to the chief cause, which we shall see later puts a practical 

 limit to very high speeds in mechanical locomotion, namely, the 

 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 center — this effective work is 



