First results of observations of star declinations on the Pulkovo horizontal meridian circle

The preliminary results of the first determinations of star declinations by the differential method, carried out on a horizontal meridian circle (HMC) of two tubes, are presented. It is shown that the HMC system represented in the form of a distribution of points of the equator in declination, varies little with temperature, and after allowance for instrumental errors, it coincides for the two tubes to within the observational accuracy. Averaging over the two tubes of the HMC system reveals no variation in declination to within plus or minus 0.3 arcsec, and this leads to the principal conclusion that instrumental flexure of the HMC is very small or even absent. The precision characteristics of the photoelectric ocular micrometer of the HMC, the automatic circle-reading system, the pendulum mirror horizon, and the system for remote setting of the HMC mirror in zenith distance are given.