108 PHILOSOPHICAL THOUGHT. 



the scientific worker; that he lives in much greater 

 intimacy with it, and that, above the endless changes and 

 the bewildering detail, he finds it difficult or impossible to 

 rise to a conception of that regularity, uniformity, and 

 continuity which seem to be the first conditions of all 

 human certainty. 



It may here be mentioned that in the course of that 

 searching investigation, that scrutiny to which scientific 

 thought has been subjected during the nineteenth cen- 

 tury, we have come to see that those three requisites of 

 scientific certainty, those foundations of natural know- 

 ledge regularity, uniformity, and continuity, may after 

 all be to a large extent fictitious, having their origin 

 not so much in nature itself as in the powers and 

 limitations of the human mind. I have had occasion to 

 point to this in the earlier part of this History, and to 

 point out how the degree of certainty in the various 

 sciences depends almost entirely upon the amount of 

 abstraction to which they have attained, that the closer 

 we approach the single facts, things and phenomena of 

 nature as they present themselves in the actual world 

 itself and not in the artificial world such as the labo- 

 ratory, the museum, or the dissecting-room, the more 

 we come, so to speak, to close quarters with nature 

 itself, the more uncertain and imperfect becomes our 

 knowledge. Such is notably the case with the phe- 

 nomena of Life, be it in the Individual or in Society. 



But there is another equally important feature 

 peculiar to scientific knowledge, which has become more 

 and more prominent during the nineteenth century, 

 and with which the scientific student will always defy 



