332 



INDttCTlON. 



§ 7. It is necessary, before quitting 

 the subject of hypotheses, to guard 

 against the appearance of reflecting 

 upon the scientific value of several 

 branches of physical inquiry, which, 

 though only in their infancy, I hold 

 to be strictly inductive. There is a 

 great difference between inventing 

 agencies to account for classes of phe- 

 nomena, and endeavouring, in con- 

 formity with known laws, to conjec- 

 ture what former collocations of known 

 agents may have given birth to indi- 

 vidual facts still in existence. The 

 latter is the legitimate operation of 

 inferring from an observed effect the 

 existence, in time past, of a cause 

 similar to that by which we know it 

 to be produced in all cases in which 

 we have actual experience of its origin. 

 This, for example, is the scope of the 

 inquiries of geology ; and they are no 

 more illogical or visionary than judi- 

 cial inquiries, which also aim at dis- 

 covering a past event by inference 

 from those of its effects which still 

 subsist. As we can ascertain whether 

 a man was murdered or died a natural 

 death from the indications exhibited 

 by the corpse, the presence or absence 

 of signs of struggling on the ground 

 or on the adjacent objects, the marks 

 of blood, the footsteps of the sup- 

 posed murderers, and so on, proceed- 

 ing throughout on uniformities ascer- 

 tained by a perfect induction without 

 any mixture of hypothesis, so if we 

 find, on and beneath the surface of 

 our planet, masses exactly similar to 

 deposits from water, or to results of 

 the cooling of matter melted by fire, 

 we may justly conclude that such has 

 been their origin ; and if the effects, 

 though similar in kind, are on a far 

 larger scale than any which are now 

 produced, we may rationally and 

 without hypothesis conclude, either 

 that the causes existed formerly with 

 greater intensity, or that they have 

 operated during an enormous length 

 of time. Further than this no geolo- 

 gist of authority has, since the rise of 

 the present enlightened school of geolo- 

 gical speculation, attempted to go. 



In many geological inquiries it 

 doubtless happens that though the 

 laws to which the phenomena are 

 ascribed are known laws, and the 

 agents known agents, those agents 

 are not known to have been present 

 in the particular case. In the specu- 

 lation respecting the igneous origin 

 of trap or granite, the fact does not 

 admit of direct proof, that those sub- 

 stances have been actually subjected 

 to intense heat. But the same thing 

 might be said of all judicial inquiries 

 which proceed on circumstantial evi- 

 dence. We can conclude that a man 

 was murdered, though it is not proved 

 by the testimony of eyewitnesses that 

 some person who had the intention of 

 murdering him was present on the 

 spot. It is enough, for most pur- 

 poses, if no other known cause could 

 have generated the effects shown to 

 have been produced. 



The celebrated speculation of La- 

 place concerning the origin of theearth 

 and planets participates essentially 

 in the inductive character of modern 

 geological theory. The speculation 

 is, that the atmosphere of the sun 

 originally extended to the present 

 limits of the solar system ; from 

 which, by the process of cooling, it 

 has contracted to its present dimen- 

 sions ; and since, by the general 

 principles of mechanics, the rotation 

 of the sun and of its accompanying 

 atmosphere must increase in rapidity 

 as its volume diminishes, the increased 

 centrifugal force generated by the 

 more rapid rotation, overbalancing 

 the action of gravitation, has caused 

 the sun to abandon successive rings 

 of vaporous matter, which are sup- 

 posed to have condensed by cooling, 

 and to have become the planets. 

 There is in this theory no unknown 

 substance introduced on supposition, 

 nor any unknown property or law 

 ascribed to a known substance. The 

 known laws of matter authorise us to 

 suppose that a body which is con- 

 stantly giving out so large an amount 

 of heat as the sun is miist be pro- 

 gressively cooling, and that, by the 



