1 78 APPENDIX, 



the board, etc. If we continue to break it we shall 

 always have smaller particles of chalk, never any- 

 thing else. Thus men generalised from their com- 

 moner experiences, and got the idea that all things 

 are built up of small parts or molecules. Anaxagoras 

 (/oth Olympiad), from experiences such as those just 

 described, in all probability arrived at his theory of 

 elements (homceomeriae), viewing all things as built 

 up of elementary things of the same nature, flesh and 

 blood of elements of flesh and blood, etc. Similar 

 views are held to the present day, and are an expres- 

 sion of the fact that you can break most things into 

 similar but smaller parts. Quoting from Tait's 

 "Properties of Matter," 1885, p. 21, we find: "But 

 the really extraordinary fact, already known in this 

 part of our subject, is the apparently perfect similarity 

 and equality of any two particles of the same kind of 

 gas, probably of each individual species of matter, 

 when it is reduced to a state of vapour. Of such 

 parts, therefore, whether they be further divisible or 

 not, each species of solid or liquid must be looked 

 upon as built up." It will be noted that the moderns 

 would make a distinction which the ancievits did not ; 

 a modern will speak of a molecule of a gas or of in- 

 candescent iron, but he hesitates before speaking of a 

 molecule of an ordinary solid at ordinary temperature, 

 and would certainly, if an exact thinker, never dream 

 of speaking of a molecule of wood or flesh or bone. 

 If we carefully prepare as perfect a cylinder of wood 

 as we may wish, and divide it into two equal parts, 

 these (unlike the piece of chalk or iron) will not be 



