234 CHEMICAL DISCOVERY AND INVENTION 



suit from contact with a molecule the size of the particle must 

 be small, that is of the same order as the size of the molecule. 

 The movements executed by the Brownian particles may there- 

 fore be supposed to be very similar to those of the molecules 

 themselves. An idea of their character may be gained from the 

 adjoining figure which was obtained by observing the positions 



FIG. 66. BROWNIAN MOVEMENT. 

 Paths of three separate granules. 



of three granules every 30 seconds. These positions are then 

 joined, in the diagram, by straight lines. 



Investigations of the kind just described have assumed a posi- 

 tion of great interest and importance within the last few yearo. 



Something is at last beginning to be understood regarding the 

 constitution of that peculiar state of matter to which the name 

 " colloid " has been given. To Thomas Graham (at one time 

 Professor of Chemistry at University College, London, and later 



