668 THE PKINCIPLES OF SCIENCE. [CHAP. 



Similarly, the opinions of geologists have been altered by 

 the discovery of the Eozob'n in the Laurentian rocks of 

 Canada ; it was previously held that no remains of life 

 occurred in any older strata than those of the Cambrian 

 system. As the examination of the strata of the globe 

 becomes more complete, our views of the origin and suc- 

 cession of life upon the globe must undergo many changes. 



Undassed Exceptions. 



Al every period of scientific progress there will exist a 

 multitude of unexplained phenomena which we know not 

 how to regard. They are the outstanding facts upon 

 which the labours of investigators must be exerted, the 

 ore from which the gold of future discovery is to be ex- 

 tracted. It might be thought that, as our knowledge of 

 the laws of nature increases, the number of such exceptions 

 should decrease ; but, on the contrary, the more we know 

 the more there is yet to explain. This arises from several 

 reasons ; in the first place, the principal laws and forces in 

 nature are numerous, so that he who bears in mind the 

 wonderfully large numbers developed in the doctrine of 

 combinations, will, anticipate the existence of immensely 

 numerous relations of one law to another. When we are 

 once in possession of a law, we are potentially in possession 

 of all its consequences ; but it does not follow that the 

 mind of man, so limited in its powers and capacities, can 

 actually work them all out in detail. Just as the aberra- 

 tion of light was discovered empirically, though it should 

 have been foreseen, so there are multitudes of unexplained 

 facts, the connexion of which with laws of nature already 

 known to us, we should perceive, were we not hindered by 

 the imperfection of our deductive powers. But, in the 

 second place, as will be more fully pointed out, it is not to 

 be supposed that we have approximated to an exhaustive 

 knowledge of nature's powers. The most familiar facts 

 may teem with indications of forces, now secrets hidden 

 from us, because we have not mind-directed eyes to 

 discriminate them. The progress of science will consist 

 in the discovery from time to time of new exceptional 

 phenomena, and their assignment by degrees to one or 

 other of the heads already described. When a new fact 



