and find the corresponding values of
. This can be done in two ways. First, we may hold the pressure constant and choose smaller and smaller drops with which to work, or we may work with drops of much the same size but vary the pressure of the gas in which our drops are suspended, for the mean free path
is evidently inversely proportional to the pressure.
Both procedures were adopted, and it was found that a given value of
always corresponded to a given value of
, no matter whether