Consideratious on the Problem of Latitude Variation. 9 



not appear, owing to a reason to hu discussed later. And, even 

 if the effect of this were considérai )lc, it would be ehminatcd from 

 the final result, as the relative position of the observer and the 

 levels does not change in the two positions of the telescope. There- 

 fore I did not try to make any further investigation on this point. 



As to the second phenomenon, we can take into consideration 

 the following three causes. — 



i. Flexure of the telescope, 

 ii. Differential change of the telescope stand. 



iii. Gradual tilting of the pier and the ground. 



A gradual change of the flexure of the telescope tube may be 

 probal)le. according to K. Hirayama^\ although it does not seem to 

 be very effective, considering the structure of our zenith telescope. 

 And this cannot l>e the sole cause ; for if it were, the displacement 

 of the bubble must be wholly attributed to a cause in the level itself, 

 as the flexure of the telescope would by no means api)ear on the 

 level. As this consequence is of course unnatural and also im- 

 probable, we are led to seek some other causes. At any rate, as 

 the effect of flexure on latitude from the observation of a star pair, 

 when we 1)egin Avith the southerly star, has the tendency to cancel 

 that from a star pair, when we begin with the noi'therl}^ star, the 

 final effect will tend to vanish, if these distinct pairs are impartial- 

 ly contained in a group. Moreover, even if there be a residual, it 

 would be eliminated I)y the chain method reduction, as it can l>e 

 looked upon as persistent with the star pairs. So I shall not at- 

 tempt any further discussion of this subject. 



As to tlie disturbance of the telescope mounting, I can first 

 of all take into consideration the thermal effect of the observer's 

 body and the unsymmetry of the meteorological conditions with 

 respect to the instrument. In winter the wind blows mostly from 

 the north, producing a draught of cold air ; in summer, the south 

 wind prevails, forming a warm air current. These disturbances, 

 combined together, may cause a certain unsymmetrical distribution 

 of heat in the telescope mounting in some way, and therefore a 

 certain change in the inclination of the telescope. As the heating 



li Astronomische Nachrichten, Xr. 4332. 



