SKETCH TOWARDS A THEORY OF THE EARTH. 411 



In both cases, in stating what I believe to be know- 

 ledge, and what seems to me ignorance, I would fain 

 think that I have had but one object, the pursuit of 

 truth. Whether hypotheses are the result of ignorance, 

 or vanity, or enthusiasm, I shall not here enquire; but 

 let the proposer of a theory, in any science, ask himself, 

 whether, in undertaking to teach others, he has laboured 

 to acquire a good conscience, whether he rests his 

 claims to belief, on industry, a cool judgment, and the 

 preference of truth to the gratification of vanity : on 

 the love of Truth above all things. To mislead, in mo- 

 rals, is acknowledged wrong ; to do this wilfully, is 

 admitted criminality. Can the same conduct be inno- 

 cent, far more, justifiable, in physical science? He who 

 checks the progress of human knowledge, obstructs 

 human improvement and human good: he is not al- 

 ways even an indirect source of evil. 



But what is Truth? all make the same profession. 

 Yes, there is a test by which it may be tried, and I give 

 it in the words of one whose soundness of judgment 

 will not easily be disputed. " How a man may know 

 whether he be so in earnest, is worth enquiry ; and I 

 think there is one unerring mark of it, viz., the not 

 entertaining any proposition with greater assurance 

 than the proofs it is built on will warrant." If, through- 

 out this work, I have taken this rule for a guide, so 

 have I striven to follow it; and if I have kept it in 

 view in this sketch of a Theory of the Earth, I may 

 also add, from the same writer, that " he who by in- 

 difterency for all but truth suffers not his assent to go 

 faster than his evidence nor beyond it, will learn to ex- 

 amine, and examine fairly, instead of presuming." He 

 indeed who would declare this of himself, ought to 

 possess the powers, the conscience, and the self-know- 

 ledge of Locke; but it were well for philosophy if all 



