Soon after the invention of the microscope
in the 17th century it was observed that pollen immersed in a fluid of its own
specific weight does not stay calmly suspended but rather moves about in
a highly irregular fashion, and never stops. The English physicist Brown
studied this phenomenon extensively in the early part of the 19th century
and found some systematic behavior: the motion is the more pronounced the
smaller the pollen and the higher the temperature; the pollen does not aim for
any goal – rather, during any time-interval its path appears much the same as
it does during any other interval of like duration, and it also looks the same
if the direction of time is reversed. There was speculation that the pollen,
being live matter, is propelling itself through the fluid. This, however, runs
into the objection that it must have infinite energy to do so (jars of fluid with
pollen in it were stored for up to 20 years in dark, cool places, after which the
pollen was observed to jitter about with undiminished enthusiasm); worse,
ground-up granite instead of pollen showed the same behavior.