1GO THE GENESIS OF SCIENCE. 



adjacent hedge, can describe the particular form and col 

 ours of the bird making them ; and the astronomer, who, 

 having calculated a transit of Venus, can delineate the black 

 spot entering on the sun s disc, as it will appear through 

 the telescope, at a specified hour ; do essentially the same 

 thing. Each knows that on fulfilling the requisite condi 

 tions, he shall have a preconceived impression that after a 

 definite series of actions will come a group of sensations of 

 a foreknown kind. The difference, then, is not in the funda 

 mental character of the mental acts ; or in the correctness 

 of the previsions accomplished by them ; but in the com 

 plexity of the processes required to achieve the previsions. 

 Much of our commonest knowledge is, as far as it goes, rig 

 orously precise. Science does not increase this precision ; 

 cannot transcend it. What then does it do ? It reduces 

 other knowledge to the same degree of precision. That 

 certainty which direct perception gives us respecting coex 

 istences and sequences of the simplest and most accessi 

 ble kind, science gives us respecting coexistences and se 

 quences, complex in their dependencies or inaccessible to 

 immediate observation. In brief, regarded from this point 

 of view, science may be called an extension of the percep 

 tions by means of reasoning, 



On further considering the matter, however, it will per 

 haps be felt that this definition does not express the whole 

 fact that inseparable as science may be from common 

 knowledge, and completely as we may fill up the gap be 

 tween the simplest previsions of the child and the most re 

 condite ones of the natural philosopher, by interposing a 

 series of previsions in which the complexity of reasoning 

 involved is greater and greater, there is yet a difference 

 between the two beyond that which is here described. And 

 this is true. But the difference is still not such as enables 

 us to draw the assumed line of demarcation. It is a differ 

 ence not between common knowledge and scientific knowl- 



