DEFINITION OF SCIENCE. 119 



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 resj^ecting 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 cm extension of the percep- 

 tions hy 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 ass\imed Hne of demarcation. It is a differ- 

 ence not between common knowledo:e and scientific knowh 



