Iß Art. 3— K. Sotome : 



Prof. J. Bonsdorff of Pulkovo Observatory. 



Dr. E. JSchoenberg of the Universit^^- Observatory at Jurjew 



(Dorpat): (transit instrument of broken type made by Repsokl). 



After all, it may be concluded that the majority of the most 



careful latitude observers (especially the international observers) 



experience a systematic shift of the level bubbles, in the same 



manner as I have already described. 



Thus I have reached the position of being able to make the 

 following resume, in so far as I have ol)tained results from the 

 al)0ve investigations: — 



In most cases the level bubbles of the zenith telescope make a 

 southward shift s^^stematically, when the observer has been 

 near the telescope for a tolerably long time, the magni- 

 tude of which varies inversely with the temperature. 

 This movement may be considered as due, partly to the 

 observer's direct effect on the level, and partly to the tilting 

 of the telescope mounting, <nving to the observer's heat disturb- 

 ance, in conjunction with some meteorological conditions. 

 The regular change in the ground from the solar radiation may 

 also contribute to the latter, altliough to a comparatively 

 slight degree. 



It may not be out of place to remark that we may expect the 

 counter effect to the above phenomenon; that is, when the observ- 

 er recedes from the instrument after a tolerably long stay near it, 

 the bubble would move back in a northerly direction towards its 

 original position, being freed from the thermal disturbance. This 

 was often experienced by some observers. It seems also to be very 

 desirable from my standpoint that hereafter the elongation observ- 

 ations of polar stars should be more frequently and regularly made 

 and the reduction performed more exhaustively, so as to throw 

 further light upon tlie subject. 



2. A theory of the motion of the level Bubbles. 



In using a screw micrometer we are accustomed to elinnnate 



