Following a brief historical introduction, a novel method for inducing and
measuring cosmic ray showers using a low-cost microcomputer-based laborator
y system is described. This reproduction of Bruno Rossi's classic experimen
t uses low counting-rate radiation monitors. The advantage of this is that
a simple AND gate can be used to trigger coincidences, which makes the work
ings of the experiment completely transparent to undergraduate students. Th
e disadvantage is that data must be taken for many days to get reasonably a
ccurate results. A simple theory is presented that models the resulting sho
wer curve quite well. (C) 2001 American Association of Physics Teachers.