, then, according to Ladenburg, the simple Stokes formula should be modified to read
Arnold found that this formula held accurately in all of his experiments in which the walls had any influence on the motion. Thus he worked under conditions under which all of the first four assumptions underlying Stokes’s Law were taken care of. This made it possible for him to show that the law held rigorously when the fifth assumption was realized, and also to find by experiment the limits within which this last assumption might be considered as valid. Stokes had already found from theoretical considerations[50] that the law would not hold unless the radius of the sphere were small in comparison with
, in which
is the density of the medium,
its viscosity, and
