RANGE OF POSITIVE KNOWLEDGE. 57 



depended on these self-evidencing qualities of bodies 

 only ; for of how few of them would touch and form give 

 a complete or satisfactory description. Yet this is the 

 absolute boundary of man's positive knowledge as to 

 matter. All the other qualities he knows of it are 

 relative, the result of comparison and the perception of 

 difference and distinctiveness. Had we but one body only 

 to handle or look at, of its form and reality we could at 

 once convince ourselves ; but its colour, if it have any, 

 depends on the light under which it is seen or the colours 

 by which it is surrounded, and the fact whether it is 

 qualified to reflect the primary, or only the complementary 

 of the colour or light under which it is seen. Its weight, 

 its size, its temperature, &c., are all equally relative, and 

 only capable of being negatively ascertained. It is not so 

 heavy, so large, or so warm as this, or not so light, so 

 small, or so cold as that object of comparison, is the whole 

 amount of our knowledge in regard to these qualities; 

 but what its absolute weight, size, or temperature is, we 

 cannot tell, for we do not know the absolute weight, size, 

 or temperature of anything ; we merely know that such 

 qualities do exist in things. 



It must hence be obvious that our knowledge of the 

 relative qualities of bodies is much more comprehensive than 

 our knowledge of their positive qualities, and that wherever 

 we are deprived of the opportunity of applying those stand- 

 ards of comparison to objects by which alone their relative 

 qualities can be determined we are helplessly thrown on 

 mere trust and assumption for our knowledge, and com- 

 pletely within the power of Natural Magic or appearances 

 instead of realities and at the mercy of misconception or 

 delusion instead of accuracy. Indeed, so much of our 

 knowledge lies within this region, guarded only by our 

 power of reasoning from analogy, which is a mere 

 intellectual extension of our means of comparison and 



