SCIENCE AND ORDINARY KNOWLEDGE, 150 



arc not practically identical ; there arises the question 

 Wliat is the relationship that exists between them? .A 

 partial answer to this question may be drawn from the il 

 lustrations just given. On reconsidering them, it will be 

 observed that those portions of ordinary knowledge which 

 are identical in character with scientific knowledge, com 

 prehend only such combinations of phenomena as are direct 

 ly cognizable by the senses, and are of simple, invariable 

 nature. That the smoke from a fire which she is lighting 

 will ascend, and that the fire will presently boil water, are 

 previsions which the servant-girl makes equally well with 

 the most learned physicist ; they are equally certain, 

 equally exact with his ; but they are previsions concerning 

 phenomena in constant and direct relation phenomena 

 that follow visibly and immediately after their antecedents 

 phenomena of which the causation is neither remote nor 

 obscure phenomena which may be predicted by the sim 

 plest possible act of reasoning. 



If, now, we pass to the previsions constituting what is 

 commonly known as science that an eclipse of the moon 

 will happen at a specified time ; and when a barometer is 

 taken to the top of a mountain of known height, the mer 

 curial column will descend a stated number of inches ; that 

 the poles of a galvanic battery immersed in water will give 

 off, the one an inflammable and the other an inflaming gas, 

 in definite ratio we perceive that the relations involved 

 are not of a kind habitually presented to our senses ; that 

 they depend, some of them, upon special combinations of 

 causes ; and that in some of them the connection between 

 antecedents and consequents is established only by an ela 

 borate series of inferences. The broad distinction, there 

 fore, between the two orders of knowledge, is not in their 

 nature, but in their remoteness from perception. 



If we regard the cases in their most general aspect, wo 

 see that the labourer, who, on hearing certain notes in the 



