To seek the periodicity of air temperature the author calculated some correlation coefficients. The materials in use are the meteorological records extending over the period more than 55 years observed at Hirosima, Wakayama, Kyôto, Tôkyô, Hakodate and Nemuro.
The correlation coefficient between the mean annual temperatures considered at time s (measured in year) and at an interval of time i later is
where Δθ is the difference between the average temperature taken over the whole period and the mean temperature of an year considered.
The obtained results are as follows: γ₂₇ and γ₃₁ take the relatively high negative values and γ₂₄ relatively high positive values. Above all γ₂₇ take -0.42_??_-0.47 expect γ₂₇ obtained at Hakodate.