96 



SOIL CONDITIONS AND PLANT GROWTH 



a chronograph and causes a second weight to fall into the pan, 

 thereby restoring the balance to its original position (Fig. 14). 

 The process is repeated when the weight of sediment again 

 just exceeds the weight on the pan. 



The second step consists in calculating from the known 



Fig. 14. — Sven Odin's apparatus for mechanical analysis of soil diagrammatically 



represented (218c). 



laws of motion of solids in fluids the mass or number of 

 particles of any given radius present in the soil : but as the 

 actual particles are very irregular in shape it is necessary to 

 adopt an " equivalent " or " effective " radius, i.e. the radius of 

 a sphere which would fall with the same velocity as the particle. 



