EXCEPTIONAL PRESUMES A. 337 



(muriatic acid) was found to contain no oxygen the theory 

 had to be relinquished. Berzelius' theory of the dual 

 formation of chemical compounds has met a similar 

 fate. 



It is obvious that all conclusive experimenta crucis 

 constitute real exceptions to the supposed laws of the 

 theory which is overthrown. Newton's corpuscular theory 

 of light was not rejected on account of its absurdity or 

 inconceivability, for in these respects it is, as we have 

 seen, far superior to the undulatory theory. It was re- 

 jected because certain small diffraction fringes of colour 

 did not appear in the exact place and of the exact size 

 which calculation showed that they ought to appear 

 according to the conditions of the theory (vol. ii. pp. 145- 

 151). One single fact clearly irreconcilable with a theory 

 involves its total rejection. In the greater number of 

 cases, what appears to be a fatal exception, may be after- 

 wards explained away as a singular or disguised result of 

 the very laws with which it seems to conflict, or as due to 

 the interference of extraneous causes ; but if we fail thus 

 to reduce the fact to congruity, it remains more powerful 

 than any theories or any dogmas. 



Of late years not a few of the favourite doctrines of 

 geologists have been rudely destroyed. It was the general 

 belief that human remains were to be found only in those 

 deposits which are actually in progress at the present day, 

 so that the creation of man appeared to have taken place 

 at the beginning, as it were, of this geological age. The 

 discovery of a single worked flint in older strata and in 

 connexion with the remains of extinct mammals was suf- 

 ficient to explode such a doctrine. Similarly, the opinions 

 of geologists have been altered by the discovery of the 

 Eozoon in the Laurentian rocks of Canada ; it was pre- 

 viously held that no remains of life occurred in any older 

 strata than those of the Silurian system. As the exami- 



VOL. n. z 



