  An observation of seasonal variations in underground muon rate, $R_{\mu}$,
has been performed at Soudan, MN, by the MINOS Far Detector. The four percent
fluctuation seen over three years was highly correlated to the temperature
variations of the upper atmosphere. The coefficient relating variations in
temperature to variations in muon rate was found to be: $\alpha_T =
(T/R_{\mu})(\partial R_{\mu}/ \partial T) = 0.87 \pm 0.03$, which is near the
expectation of 0.91.
