We report the first observations of the P-3(1)-P-3(0) line of atomic c
arbon in the dark cloud TMC-1. Additionally, to compare with CO, we ob
served (CO)-C-13(2-1), (CO)-O-18(2-1) and C-17 O(2-1). The lines were
observed at five positions perpendicular to the molecular ridge close
to the cyanopolyyne peak. Optical depth effects render the determinati
on of atomic carbon column densities difficult, so only lower limits o
f about 10(17) cm(-2) are reported. However, the widths and shapes of
the carbon lines strongly suggest high optical depths, which would be
an argument in favor of the existence of atomic carbon deep inside mol
ecular clouds. A comparison of the observed intensities with the inten
sities predicted by a photochemical model of the cloud shows a reasona
bly good agreement, giving confidence in our understanding of the phys
ical and chemical processes at the edges of dark clouds.