Considerations on the Problem of Latitude Variation. 15 



winter value coines out too large, l)ut the summer value too small, 

 giving finally too large a tempei'ature coefficient. 



Dr. G. Bemporad of the International Latitude Station at 

 Carloforte reported that his instrument showed variations during 

 elongation observations, but that the sense was not systematic. 

 However, Dr. V. Fontana, the director of the station, wrote me 

 afterwards that he had l)egun some researches on the problem of 

 the systematic sliift of the level bubbles, and desired to know ni}^ 

 results. 



Dr. F. E. Ross of the Gaithersburg Latitude Observatory in- 

 formed me that he experienced a similar phenomenon, and con- 

 sidered it to be principally due to a temperature effect in the 

 ground, which usually shows a progressive change one way or the 

 other. 



Dr. E. L Yowell of Cincinnati Observatory favoured me with 

 a letter, stating that his telescope shows a similar tendency. He 

 ascribes that effect to the heat radiation from the observer and 

 the reading lamp. 



Dr. ^V. F. Meyer of the Latitude Observatory at Ukiah kindly 

 reported that his own experience was limited, but that his predecessor, 

 Dr. Schlesinger, had observed the same tendency. The following 

 was extracted from the record book, which gives Dr. Schlesinger' s 

 opinion in the matter: '' there is reason to believe, from an inspec- 

 tion of the results, that these changes in the levels are not wholly 

 due to a real change of inclination of the telescope. No doubt the 

 presence of the observer for so long a period at one side of the 

 levels has an injurious effect upon the levels." 



At Union Oljservatory, Johannesburg (Astronomer, Prof. R. 

 I. Innes), the method of polar star elongations was not employed. 



At Kasan Observatory (Dr. i\L A. Gratschew) the instrument 

 and method were different. 



The following astronomers have kindly let me know that they 

 experienced no systematic movement of the level bubbles. 



Prof. E. Doolittle of Flower Astronomical Observatory, 



University of Pennsylvania. (Warner ct Swasey's zenith 



telescope). 



