24 THE FOUNDATION Part 1 



Brownian movement. This motion is an irregular agitation of particles ol 

 difTerent sizes. The molecules constantly jostle against relatively huge par- 

 ticles, striking them unevenly on one side or another. Many of them are very 

 small molecules and others are large molecules. The molecular motion is 

 invisible, but that of the larger particles is evident with the high power of 

 the microscope. The motion occurs in gases, fluids, and especially in colloids 

 including protoplasm. It is common in the vacuoles of algae and protozoans 

 (Fig. 2.13). It was discovered in 1827 by Robert Brown, an English botanist, 

 who saw the motion in a fluid in which pollen grains were suspended. Like 

 other diffusions, Brownian movement is an example of kinetic energy. 



