150 GENERAL YIEW AND BASIS OF SCIENTIFIC RESEARCH. 



quantitative conditions. It was by means of quantitative 

 measurement that Newton discovered the qualitative truth 

 of the universal action of gravity ; and some qualitative 

 tests in chemistry can only be successfully made by adding 

 the substances to each other in proper proportions. 



A qualitative truth is not one of degree ; it is absolute. 

 In a qualitative sense, a thing must either be or not be ; 

 but the idea of accuracy is a quantitative one, and accu- 

 racy may exist in all degrees from nothing to perfection. 

 We cannot verify the exactness of the results obtained by 

 means of a more exact method, by employing a less accu- 

 rate one, because the range of uncertainty of the latter is 

 greater than that of the former. Thus it is of no use to 

 weigh in a coarse balance a light substance which has 

 already been weighed in a delicate one. It is a good plan 

 to indicate the degree of dubious accuracy by decimal 

 numbers, 



CHAPTER XII. 



PROBABILITY IN MATTERS OF SCIENCE. 



PROBABILITY is a quantitative idea, and may exist in all 

 degrees from nothing to infinity ; and as in this treatise 

 science is considered only in a qualitative aspect, I shall 

 confine myself to but a few remarks upon it. 



Probability may be defined as likelihood based upon 

 our intellectual perception of proper and sufficient evi- 

 dence. It is an idea which is dependent for its existence 

 upon the finite action of all our senses and mental powers ; 

 for if those powers were infinite, all our ideas would be as 

 certain as truth itself, and that of probability would not 

 exist. In other words, as all the existences and operations 



