306 HOUSE, GARDEN, AND FIELD 



the progress of man in the useful arts may far outstrip 

 the slow and sure course of nature, but there are very few 

 human inventions which are made suddenly, all at one 

 time. Nearly always we find upon inquiry that they are 

 founded upon ruder prototypes. A hastily-cut log is put 

 beneath the big stone, which has to be moved by few 

 hands ; a second log is added to lift the stone clear of the 

 ground, and then a third, to shift to, while the first is 

 being carried to the front ; this completes the first stage 

 of the new invention. The next thing is to fix the rollers 

 permanently to the slow and heavy cart, hitherto dragged 

 by main force over the fields. Then the rollers are in- 

 creased in diameter, and shortened in length. They become 

 thin transverse slices of trees, or built-up solid wheels, such 

 as may still be seen in some Eastern countries. The wheel 

 with nave, spokes and rim is harder to make, but it does 

 not crack so easily, and it weighs much less. A rim of 

 brass or iron gives additional strength. Then comes the 

 smooth iron bearing, and the tire shrunk on by cooling. 

 In the end we get the locomotive wheel of compressed 

 paper, with steel tire and self-acting lubricator, ready to 

 run a thousand miles a day for years together. 



This bit-by-bit discovery is just in the spirit of nature, 

 though nature is slower than man, and her adaptations 

 more exquisite. Every new idea is tested a thousand 

 times over, and only adopted for good when approved by 

 the most conclusive test, the practical superiority of those 

 who have it over those who have it not. To try all things 

 and hold fast that which is good is the essence of Natural 

 Selection. Let us work out one example as a parallel to 

 the chain of discoveries by which the locomotive-wheel 

 has been attained. 



The fishes of the sea long ago found out the advantage 

 of a nail-studded hide, and were able to arm themselves 

 with nails of suitable size and hardness, developed out of 

 the tissues of the inner skin. These nails had a broad 

 base of attachment, and a sharp point, generally pointing 



