654 VICTOR ZIEGLER 



23.4 and a viscosity of 0.011, repulsion was only noticed in the 

 finest grains. 



SUMMARY 



The results of these experiments seem to show that viscosity 

 is the factor protecting grains from wear. Viscosity will not 

 only prevent the wear of the smaller grains, but it will also act 

 as a buffer and will greatly lessen the velocity of grains when about 

 to collide with each other or with the bottom of the river. In 

 view of the results it seems improbable to the writer that grains 

 less than o. 75 mm. in diameter could be well rounded under water. 

 Well-rounded grains of about this and smaller diameter appear 

 to be the result of wind work, in which case the protecting factor, 

 viscosity, would be practically zero, so that there would be no 

 limit to the minimum size attainable by wear. 



