DEPARTMENT OF MERIDIAN ASTROMETRY.* 



Lewis Boss, Director. 



To the annual report of this Department for 1907-8 (Year Book for 1908, 

 p. 143) is appended an account of its first expedition (August to November, 

 1908) for the purpose of establishing a branch observatory for meridian 

 observations in San Luis, Argentina. This account includes the essential 

 facts in relation to the new observatory down to November 30 of that year. 



Professor Tucker, aided by Mr. Varnum, had remained in San Luis to 

 attend to the construction of the piers and buildings required for the obser- 

 vatory establishment, while I returned to Albany in order to make needed 

 investigations upon the meridian-circle, to ascertain its exact state prior to 

 its dismounting for transportation to San Luis. This, together with the 

 work of dismounting the meridian-circle and preparing it for its long jour- 

 ney, occupied much of my time from November 20 to January 20, 1909. On 

 the latter date I sailed from New York, bound for Buenos Aires, accompa- 

 nied by Assistants Roy, Zimmer, and San ford and Recorders Fair and Dela- 

 van. In addition to the meridian-circle and subsidiary apparatus, we had 

 with us a photometer for the determination of the brightness of stars in our 

 observing list that had not previously been investigated for magnitude by 

 accurate photometric methods. The stars requiring measurements by us are 

 mostly below the magnitude 6.5M. This photometer is arranged to be used 

 with an absorbing slide for purely differential observations. The telescope 

 is of 4 inches aperture ; it is very accurately and solidly mounted with equato- 

 rial movement, and is provided with good circles and other accessories for 

 convenient use. 



We arrived in Buenos Aires February 13, and the members of the staff 

 were soon sent to San Luis. On the 23d the instruments were dispatched in 

 a special car, and they were delivered at the observatory, which was then 

 fully prepared to receive them, on March i. The interval between that date 

 and April 4 was occupied in mounting, adjusting, and investigating the 

 meridian-circle, together with setting up clocks, chronographs, photometer, 

 and other apparatus. Adjustment and test observations with the meridian- 

 circle were made on several nights during the progress of mounting the 

 instrument. 



♦Address, Dudley Observatory, Albany, New York. Grant No. 542. $20,000 for 

 study of motion and structure of the stellar system of the northern and southern hemi- 

 spheres. (For previous reports see Year Books Nos. 2, 3, 4, 5, 6, and 7.) 



154 



