WALLACE O. FENN 



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described a circle the circumference of which is equal to the distance 

 which each cell or particle would have settled during the time of one 

 revolution either in a straight line or otherwise. 



Fig. 1. Diagram illustrating chance of collision between a particle, P, settling 

 down toward a cell, C. 



Fig. 2. Diagram illustrating orbits described by a particle at A and cells at b, 

 c, and dm a, rotating medium. The figure represents a cross-section of the medium 

 which is considered to be rotating clockwise. The relative direction of rotation 

 of particles and cells settling by gravity is, therefore, counter-clockwise, as indi- 

 cated by the arrows. Collisions occur at B, C, and D. Chance of collision is 

 proportional to the circumference. Abed. 



The circumference thus equals — , where n is the number of revolu- 



n 



tions per unit of time and V the velocity. Let the circle A BCD (Fig. 



2) be the orbit described by a particle, P, starting at A in the direction 



