  With an aim of examining the validity of non-LTE line-formation calculations
for the strong C I lines of multiplet 1 at 1.068-1.069 mu~m, especially in
terms of the treatment of collisions with neutral hydrogen (H I) atoms, we
computed theoretical equivalent widths (W_lambda) of these lines corresponding
to specific intensities of different angles (mu = cos(theta)) on the solar disk
under various conditions, which were then compared with the empirical W_lambda
vs. mu relations obtained from our spectroscopic observations using the
Domeless Solar Telescope at Hida Observatory. It turned out that our
observational data are almost consistent with the theoretical simulations done
with the H I collision rates computed with the classical formula, which
suggests that the necessity of its significant revision (e.g., considerable
reduction) is unlikely.
