MODELS OF MACHINES. 175 



times made that a man equally agile, with his present 

 size, would vault over the highest city-steeple, or across 

 a river as wide as the Hudson at Albany. Now, if the 

 flea were increased in size to that of a man, it would 

 become a hundred thousand times stronger, but thirty 

 million times heavier ; that is, its weight would be- 

 come three hundred times greater than its correspond- 

 ing strength. Hence we may infer that the enlarged 

 flea would be no more agile than a man ; or that, if a 

 man were proportionately reduced to the size of a flea, 

 he could leap to as great a distance. 



All this serves to illustrate in a striking manner the 

 distinction between models and machines. 



