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 THE HISTORICAL METHOD. 207 in any way affect the received methods of rational physics or the received methods of chemistry. But what shall we say of the sciences that deal with organic life ? Is it not true that zoology and botany have been invaded and transformed by the Darwinian theory, and all the speculation and investigation about the development of organic life to which it has given rise? It is certainly true that this historical biology if I may be allowed the term has wrought a change in our general conception of the actual differences in the organic world to which no parallel can be found in the sciences which deal with inor- ganic matter. For no hypothetical history that has been offered us of the inorganic world has even professed to explain the qualitative differences with which chemistry is concerned ; at least it has not professed to explain them by any method resting on an empirical basis and capable of be- ing tested by facts. Whereas the hypothetical history of the organic world which we owe to Darwin does attempt to show how differences of kind, in the matter with which it deals, have been developed out of an original identity ; or, more strictly, it aims at showing how differences in external relations, in situations and circumstances, have been taken in and transformed into differences of internal relations, differ- ences of organisation. Still, I should not exactly say that the historical or evolu- tional method of biology has invaded and transformed pre- viously existing departments of knowledge ; it rather seems to have annexed to science a new and important region, hitherto desolate and only viewed as it were from a sort of philo- sophic Pisgah as possibly destined for orderly scientific culti- vation. Whatever positive systematic knowledge of living things was thought to be given us by zoology and botany, pursued on pre-Darwinian methods, is in no way invalidated or set aside by the newer speculations : what has been invali- dated is merely the negative conception of ultimate irreduci- bility in specific and generic differences. And I may add that our knowledge of the history of life on this planet had made even this negative conception philosophically unten- able, long before Darwin's theory was produced ; for it had become evident from the geological record that we could not deal with organic as with inorganic differences of kind, by throwing them back to the inscrutable origin of all things. Our existing fauna and flora must be held to have appeared on the planet after long periods of time in which pre-existing species had lived and died out : they could not have trooped in, as we know them, on the most conveniently arranged