4 ELEMENTS OF SCIENCE 



same time equally relate to all the phenomena which 

 will thus have affected the student's senses ? What can 

 be common to them all without exception ? 



Its nature must be wide indeed, since it must be 

 common to things so different. It must be common 

 to animal life and the life of plants, to colour, to sound 

 and to motion, to the sea's waves, the action of running 

 streams, the formation of rocks and hills, and the move- 

 ments of every breeze ; to thunder and to lightning, to 

 earth and to sky, to the sun, moon, and stars, to human 

 history, the progress and decay of institutions, the 

 development of art, and even to the very thoughts 

 which deal with things so various. 



Such a combination may well at first seem utterly 

 bewildering, and yet a few very simple reflections may 

 serve to solve the puzzle. 



To know anything whatever, is to know that it is 

 distinct from something else. Two marbles, alike in 

 colour and size, shape and weight, are known with 

 perfect certainty to be distinct, though we may not be 

 able to tell one from the other. We recognise them as 

 two things of the same kind. Together they form a 

 small group composed of two objects. If now these be 

 held in the right hand, while a third marble, exactly like 

 the other two, is held in the left hand, then the contents 

 of the right hand differs from that of the left simply by 

 being " two " instead of " one " that is, by a difference 

 of number. 



But "number" is a property possessed by all the 

 things above referred to, since even thoughts, no less 

 than marbles, differ from each other numerically. Enu- 

 meration accurate enumeration is necessary for all 

 kinds of knowledge. We may feel things to be hotter or 

 colder, but if we would be accurate we must employ a 



