Framework 53 



of proportion with the short distance involved. Whoever 

 thought up the force of gravity was a pretty clever fellow, 

 but he went too far. It looks as if half, or even a quarter, of 

 its present power would have been sufficient to keep us from 

 flying off the earth into space, without being a constant 

 nuisance to us. 



The fish is more fortunate than we. The element in which 

 he lives, water, has a specific gravity almost the same as that 

 of his own body. This means that his weight is held up by the 

 water, and that it requires no effort on his part to support 

 himself. To be definite, a twenty-pound fish, even if he is 

 all lean and no fat — and most fish do have a certain amount 

 of fat and other buoyant auxiliaries — weighs only about one 

 pound in salt water. If he wants to go up, all he has to lift 

 is one pound. All the rest of his energy is free to use in other 

 ways. It is as if a 150-pound man were to find his weight 

 suddenly reduced to 7/4 pounds. If you can imagine how 

 fast this man could run or how high he could jump, you get 

 some idea of how easy it is for the fish to move about. To go 

 straight upwards, as you do when you pull yourself up a 

 rope hand over hand, is no harder for our fish than it is for 

 you to lift a 7H-pound brief-case. And if we abandon our 

 lean fish in favor of the many kinds, of which the salmon 

 is one, whose specific gravity is just about equal to water's, 

 no energy at all is devoted to weight-lifting. All he has to 

 overcome is the resistance of the water, and in this he has the 

 help of the original, and still the best, stream-lined body. 



Now, while this is all very nice for the fish, it has, in the 

 long run, been a bad thing for us. The fish's body being sup- 

 ported on all sides by the medium in which it lived, all it 

 needed in the way of a skeleton was something to keep it 

 stiff while it cleaved the water, and something for its muscles 

 to pull against. The fins had no work to do in the way of 

 holding the body up, and it was not necessary for them to 



