Using the data of observations and comparisons of time made during the period from 1933 to 1961, secular variations of the differences of the longitudes among Tokyo, Europe (the mean of 8 observatories), North-America (the mean of 2 observatories), South-America (the mean of 2 observatories), Tashkent and Zi-Ka-wei were investigated.
The results obtained from three different treatments; (a) using the annual means of the data for the whole period, (b) using five years means of the same data and (c) solving separately for two periods before and after 1950.0, show that:
(1) with great confidence we can conclude that the secular variations of the differences of longitudes between the following pairs of the observatories exist;
Tokyo-Europe : + 1.0 ms/year±0.16 (m.e.)
Tokyo-North-America : + 1.4ms/year±0.13
Tokyo-South-America : + 1.6ms/year±0.06
North-America-Europe: - 0.4ms/year±0.12
(2) for other pairs of observatories, the secular variations can not be determined from the present data with great confidence.
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