OF NATURAL PHILOSOPHY. 75 



PART II. 



OF THE PRINCIPLES ON WHICH PHYSICAL SCIENCE 

 RELIES FOR ITS SUCCESSFUL PROSECUTION, AND 

 THE RULES BY WHICH A SYSTEMATIC EXAMI- 

 NATION OF NATURE SHOULD BE CONDUCTED, 

 WITH ILLUSTRATIONS OF THEIR INFLUENCE 

 AS EXEMPLIFIED IN THE HISTORY OF ITS PRO- 

 GRESS. 



CHAPTER I. 



OF EXPERIENCE AS THE SOURCE OF OUR KNOAVLEDGE. 

 OF THE DISMISSAL OF PREJUDICES. OF THE EVI- 

 DENCE OF OUR SENSES. 



(66.) INTO abstract science, as we have before ob- 

 served, the notion of cause does not enter. The 

 truths it is conversant with are necessary ones, and 

 exist independent of cause. There may be 

 no such real thing as a right-lined triangle 

 marked out in space ; but the moment we conceive 

 one in our minds, we cannot refuse to admit the 

 sum of its three angles to be equal to two right 

 angles ; and if in addition we conceive one of its 

 angles to be a right angle, we cannot thenceforth 

 refuse to admit that the sum of the squares on the 

 two sides, including the right angle, is equal to 

 the square on the side subtending it. To maintain 

 the contrary, would be, in effect, to deny its 

 being right angled. No one causes or makes all 

 the diameters of an ellipse to be bisected in its 



