56 De Vi Physica 



impossible. To change a principle, to in- 

 troduce a new principle, a jump is absolutely 

 necessary : by gradual transition, it cannot 

 be done. A principle cannot originate 

 gradually. For example, you can have 

 sledges and you can have wheeled vehicles, 

 and any number of transitional variations 

 on either principle, within its limits. But 

 you cannot pass by gradation, by accumu- 

 lated increment, from the principle of sledge 

 to that of wheel: you must jump: no vari- 

 ation of sledges will ever produce a wheel. 

 Just so, you cannot pass by gradation from 

 sails to steam, in the navigation of ships. 

 No variety of sails will ever bring you to 

 steam. And so it is universally in Nature. 

 You cannot bridge the gap between different 

 principles of organisation. Intermediate 

 gradations cannot possibly exist. Darwin's 

 supposition that they could : his expectation 

 to find them, but for the imperfection of the 



