Kazan State university
Optical interferometers make it possible to achieve an instrumental precision about 1 mas by positional observations. It is supposed besides two-colour observations will give a value of astronomical refraction. We have attempted to estimate an accuracy of refraction calculations by formulas for the two-colour method of refraction determination used the theory of astronomical refraction for the real atmosphere (A\&A,Suppl.Ser.111) and date of meteorological fields in the meridian circle room of Engelhard observatory. The results of our Colleague Ishmukchametov investigations were used. One made measuring of vertical and horizontal gradients of the air temperature length-wise of a light ray in the course of an absolute meridian observing by a Repsold's meridian circle. The observations were fulfilled at zenith distances of 50 - 70 degrees. Our estimates show the two-colour method insufficient for to determine the astronomical refraction with the above mentioned precision. The use of the theory of astronomical refraction for the real atmosphere makes it possible to correct this situation.