RATIONALISM AND SCIENCE 227 



This quotation brings us to the point. He appears 

 to be comparing, or contrasting, if he be not putting one 

 against the other, vis., Deductive and Inductive reason. 

 He does not recognise the value of the latter in these 

 so-called " supraphysical " sciences. The former is that 

 employed by Euclid and other mathematicians. It is 

 safe for them to do so, because there are only a few 

 axioms or postulates upon which the whole of the super- 

 structures are built ; and if the steps in their logical 

 sequences of any proposition are correctly made, they 

 cannot arrive at any other conclusion than a Q. E. D. 



In astronomy the occurrence of eclipses can be fore- 

 told with accuracy hundreds of years in advance, if neces- 

 sary. 



The laws of heat, light, electricity, and magnetism are 

 known ; so that they can be trusted to do their work, and 

 utilised, as their effects are constant. But in biology it 

 is not always so. Data are more complex on which to 

 reason ; but inductive reasoning now meets the case, so 

 that to an enormous extent the conclusions of biological 

 scientists are perfectly sound and equivalent in value to 

 mathematical demonstrations. 



In astronomy it has to be trusted ; thus, I repeat, the 

 conviction that the earth revolves on its axis in twenty- 

 four hours is solely founded on inductive evidence. 

 Similarly is our knowledge of the elements in the sun 

 established on faith in the accumulation of coincidences, 

 on which probabilites are based. These are of so high 

 an order, that they force the moral conviction, and any 

 alternative becomes unthinkable. 



It is solely on inductive evidence that the Copernican 

 system has superseded the Ptolemaic. 



In biology the great doctrine of Evolution is largely 

 based upon induction ; for probabilities pour in from all 



