76 DISCOURSE ON THE STUDY 



centre. To assert the contrary, would not be to 

 rebel against a power, but to deny our own words. 

 But in natural science cause and effect are the ulti- 

 mate relations we contemplate ; and laws, whether 

 imposed or maintained, which, for aught we can per- 

 ceive, might have been other than they are. This 

 distinction is very important. A clever man, shut 

 up alone and allowed unlimited time, might reason 

 out for himself all the truths of mathematics, by 

 proceeding from those simple notions of space and 

 number of which he cannot divest himself without 

 ceasing to think. But he could never tell, by any 

 effort of reasoning, what would become of a lump 

 of sugar if immersed in water, or what impression 

 would be produced on his eye by mixing the colours 

 yellow and blue. 



(67.) We have thus pointed out to us, as the great, 

 and indeed only ultimate source of our knowledge of 

 nature and its laws, EXPERIENCE; by which we 

 mean, not the experience of one man only, or of 

 one generation, but the accumulated experience of 

 all mankind in all ages, registered in books or re- 

 corded by tradition. But experience may be ac- 

 quired in two ways : either, first, by noticing facts as 

 they occur, without any attempt to influence the 

 frequency of their occurrence, or to vary the cir- 

 cumstances under which they occur ; this is OBSERV- 

 ATION: or, secondly, by putting in action causes 

 and agents over which we have control, and pur- 

 posely varying their combinations, and noticing 

 what effects take place ; this is EXPERIMENT. To 

 these two sources we must look as the fountains of 

 all natural science. It is not intended, however, by 



