OBJECT AND LIVING ORGANISM loi 



smelt it, tested its sound and tasted it. Then he noted down 

 all the properties observed, and from these data he described 

 the substance as exactly as possible, in order to distinguish it 

 from others. 



Very early the theory of the four elements was established. 

 But the knowledge that every substance has three states 

 of aggregation controlled by heat was no more than a vague 

 presentiment lying at the basis of this theory. 



The unreliability of the tests, and especially of those 

 for the intensities of the several qualities, led gradually to 

 the introduction of other properties admitting of more 

 certain determination. Thus, in order to get away from 

 direct testing of heat, use was made of the expansion of 

 bodies, and the thermometer was invented. To measure 

 weight, the movement of the balance was employed, and that 

 fixed the standard. 



To test hardness, a series of special substances was chosen, 

 each of which would just scratch the others. 



In place of testing by smell and taste came later the study 

 of the relationships of those substances which either com- 

 bined with one another or separated off from one another. 



Thus by imperceptible degrees the whole study passed 

 from the domain of the other sense-organs to that of the eye. 

 AU our apparatus has reference to the eye, and especially 

 since in chemistry the testing by sound has fallen more and 

 more into disuse. 



Small wonder if, in the course of time, the conception 

 of what a substance reaUy is has become completely changed. 

 The study of the forms of crystals, which furnishes what is the 

 most reliable characteristic of substances, has been mainly 

 responsible for the present tendency to explain all the pro- 

 perties of matter on the basis of an invisible miniature struc- 

 ture. It is in accordance with this that stereochemistry has 

 developed, a science which traces the affinities of substances to 



