2 THE PRINCIPLES OF SCIENCE. [CHAP. 



the old, recognises essential identity, even when disguised 

 by diverse circumstances, and expects to find again what 

 was before experienced. It must be the ground of all 

 reasoning and inference that what is true of one tiling will 

 be true of its equivalent, and that under carefully ascertained 

 conditions Nature repeats herself. 



Were this indeed a Chaotic Universe, the powers of mind 

 employed in science would be useless to us. Did Chance 

 wholly take the place of order, and did all phenomena 

 come out of an Infinite Lottery, to use Condorcet's ex- 

 pression, there could be no reason to expect the like result 

 in like circumstances. It is possible to conceive a world 

 in which no two things should be associated more often, in 

 the long ran, than any other two things. The frequent 

 conjunction of any two events would then be purely 

 fortuitous, and if we expected conjunctions to recur con- 

 tinually, we should be disappointed. In such a world we 

 might recognise the same kind of phenomenon as it ap- 

 peared from time to time, just as we might recognise a 

 marked ball as it was occasionally drawn and re-drawn 

 from a ballot-box ; but the approach of any phenomenon 

 would be in no way indicated by what had gone before, 

 nor would it be a sign of what was to come after. In such 

 a world knowledge would be no more than the memory of 

 past coincidences, and the reasoning powers, if they existed 

 at all, would give no clue to the nature of the present, and 

 no presage of the future. 



Happily the Universe in which we dwell is not the 

 result of chance, and where chance seems to work it is 

 our own deficient faculties which prevent us from recog- 

 nising the operation of Law and of Design. In the material 

 framework of this world, substances and forces present 

 themselves in definite and stable combinations. Things 

 are not in perpetual flux, as ancient philosophers held. 

 Element remains element; iron changes not into gold. 

 With suitable precautions we can calculate upon finding 

 the same thing again endowed with the same properties. 

 The constituents of the globe, indeed, appear in almost 

 endless combinations ; but each combination bears its fixed 

 character, and when resolved is found to be the compound 

 of definite substances. Misapprehensions must continually 

 occur, owing to the limited extent of our experience. We 



