On the accuracy of the Refraction Tables of Pulkovo Observatory,fifth edition

A systematic deviation has been found of the refraction given in Pulkovo Tables, fifth edition, from the standard refraction calculated for the same ground level meteorological conditions by the procedure described in one of our previous papers. This deviation, negative for zenith distances smaller than 75° and positive for zenith distances larger than 80°, is considerably greater than the error proven to be admissible for the pure refraction determined in the latter way. The value of deviation is of the order of 0″.03 already at z₀ = 45°. For zenith distances smaller than 75° the deviation originates almost exclusively from unsufficiently accurate corrections for the air humidity. For larger zenith distances the deviation originates mainly from the correction for the air temperature and contributions of the remaining corrections can partly compensate for it. In conclusion a proposition of a new unique standard of the pure refraction is stated.