250 REASONING. 



positions forming a train of reasoning, viz. that of enabling 

 us to arrive in an indirect method, by marks of marks, at such 

 of the properties of objects as we cannot directly ascertain (or 

 not so conveniently) by experiment We travel from a given 

 visible or tangible fact, through the truths of numbers, to the 

 facts sought. The given fact is a mark that a certain relation 

 subsists between the quantities of some of the elements con- 

 cerned ; while the fact sought presupposes a certain relation 

 between the quantities of some other elements : now, if these 

 last quantities are dependent in some known manner upon the 

 former, or vice versa, we can argue from the numerical relation 

 between the one set of quantities, to determine that which 

 subsists between the other set ; the theorems of the calculus 

 affording the intermediate links. And thus one of the two 

 physical facts becomes a mark of the other, by being a mark 

 of a mark of a mark of it. 



