318 THE PRINCIPLES OF SCIENCE. 



Division of the Subject. 



The general subject of quantitative investigation will 

 have to be divided into several parts. We shall, firstly, 

 consider the means at our disposal for measuring phe 

 nomena, and thus rendering them more or less amenable 

 to mathematical treatment. This task will involve an 

 analysis of the principles on which accurate methods of 

 measurement are founded, forming the subject of the 

 remainder of the present chapter. As measurement, how 

 ever, only yields ratios, we have in the next chapter 

 (XIV) to consider the establishment of unitary mag 

 nitudes, in terms of which our results may be expressed. 

 As every phenomenon is usually the sum of several dis 

 tinct quantities proceeding from different causes, we have 

 next to investigate in Chapter XV the methods by which 

 we may disentangle complicated effects, and refer each 

 part of the joint effect to its separate cause. 



It yet remains for us in subsequent chapters to treat of 

 quantitative induction, properly so called. We must 

 follow out the inverse logical method, as it presents itself 

 in problems of a far higher degree of difficulty than those 

 which treat of objects related in a simple logical manner, 

 and incapable of merging into each other by addition and 

 subtraction. 



Continuous Quantity. 



The phenomena of nature are for the most part mani 

 fested in quantities which increase or decrease continu 

 ously. When we inquire into the precise meaning of 

 continuous quantity, we find that it can only be described 

 as that which is divisible without limit. We can divide 

 a millemetre into ten, or one hundred, or one thousand, or 

 ten thousand parts, and mentally at any rate we can carry 



