DEPARTMENT OF MERIDIAN ASTROMETRY.^ 



Benjamin Boss, Director. 

 During the past year a study of the discordances in meridian observations 

 has thrown considerable hght on their nature. The effect of differential 

 refraction upon observations has received special attention. While it is 

 certain that this phenomenon accounts for many of the discordances noted 

 in all meridian observations, which have heretofore been taken out by empiri- 

 cal means if they have been removed at all, the work of the past year has 

 shown that the elimination of these effects by formula would unduly delay 

 the publication of the San Luis and Albany observations, from which the 

 greater part of the discordances have already been taken out empirically. 

 Consequently, it has been decided to publish these observations without 

 employing differential refraction. 



REDUCTIONS OF OBSERVATIONS. 

 The San Luis observations in zenith distance have been completely reduced 

 and the mean dechnations for 1910.0 are ready to be put into manuscript. 

 The right ascensions are also reduced to the point where a study of discordant 

 series is being made, preparatory to reducing to the mean position for 1910.0. 

 These should be ready to put into manuscript within a few months. The 

 reductions of the Albany declinations are in an advanced stage, but consider- 

 able work remains to be done on the right ascensions. 



STELLAR PARALLAX. 



An attempt has been made to determine the systematic errors of the Mount 

 Wilson spectroscopic parallaxes, based upon their direct comparison with 

 the trigonometric parallaxes. This method might be presupposed to include 

 a regression factor. Independent evidence is furnished by the data secured 

 from moving clusters of stars, which supports the corrections to the Mount 

 Wilson system derived by the direct-comparison method for the region cover- 

 ing the smaller parallaxes. The agreement is possibly due to the fact that 

 the regression factor has not been taken into account in the formation of the 

 curves on which the Mount Wilson system is based. The corrections derived 

 indicate that for the more distant stars, those whose parallax is less than 

 0''02, this system assigns too great a distance, while the nearer stars, parallax 

 0''02 to 0''12, have been placed too near. There are few stars with parallaxes 

 over 0T12, representing our nearest neighbors in space, but the evidence 

 deduced from the observed material indicates a rather sharp break in the 

 Mount Wilson system at this point. The apparent break may possibly be 

 due to the fortuitous distribution of errors, and to the fact that the correlation 

 curves for faint absolute magnitudes do not follow the form of the curves 

 for the brighter magnitudes. When the material is divided according to 

 type there appear to be systematic differences between the corrections 

 indicated for different types. 



The Mount Wilson parallaxes, corrected for systematic error, have been 

 employed in deriving the corrections to other series of parallaxes. These 

 are in essential agreement with the corrections published at Mount Wilson. 

 In a former investigation by this Department, corrections to the trigono- 

 metric parallaxes varying with the right ascension were indicated. A 



Address: Dudley Observatory, Albany, New York. 



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