3 6 THE POPULAR SCIENCE MONTHLY. 



In periods of transition we can well imagine that an elasticity in 

 stationary circumstances, usually all but dormant in an organism, 

 comes into play with all its power; and hence that the type fit for 

 the new conditions is, comparatively speaking, soon formed and fixed. 

 We may thus understand how it is that a wide diversity among liv- 

 ing forms has been brought about, and why it is that few fossils in- 

 termediate between them have been discovered. Some very striking 

 ones have been unearthed, but it would be an unwarrantable die-res- 

 sion to describe them in a paper of these limits. 



The remote extremes which may be joined together by gentle and 

 imperceptible modifications are well illustrated in the facts of ordinary 

 growth. Newton had once to be taught that two and two make four, 

 yet from that day to the culmination of his powers there was no ab- 

 rupt accession of knowledge or insight. He came by steady advances 

 from the ignorance of a babe to the full stature of the first physical 

 philosopher in Europe. 



All this teaches us the supreme importance of looking at things 

 in their dynamic as well as in their static aspect ; of regarding the 

 mechanics not less earnestly than the geometry of Nature. For dif- 

 ferences in degree may gradually accumulate until they become dif- 

 ferences in kind. We have seen how various sources of obscurity may 

 veil processes of genesis, and lead any but a minute and careful ob- 

 server to mistake a new form for a new identity. We have noticed 

 how the possession of qualities usually in extremes may conceal the 

 fact that the qualities are general as in the magnet, which is but an 

 exaggerated case of any mass whatever. 



We have noticed how the vast differences in the time required in 

 transmutation may tend to confuse the similarity of two cases of a 

 law. The embrowning of a pine fence in the course of years is due to 

 the same cause which chars in a few minutes the same wood when 

 used as fuel. We have remarked, also, the enormous differences in 

 the stability of natural forces : some of them, as heat, are metamor- 

 phosed with great difficulty ; others, as electricity, are of very weak 

 permanence ; and others, again, in whose existence we have good 

 reasons to believe, are too evanescent to be detected by the keenest 

 scrutiny. 



It has also appeared that mere complexity of resultant lines, as 

 simple forces interact, may yield the erroneous supposition that new 

 and higher causes than the real ones have come into action. 



It has been briefly stated how diverse properties merge into one 

 another, and various consistencies overpass the bounds of common 

 definition ; and, leaving the region of fact for that of speculation, it 

 has been shown how the principle of continuity may account for the 

 genesis of our chemical elements, and the transfer of impulses across 

 the diameter of the heavens. 



All these facts, probabilities, and suggestions, lead to the convic- 



