homogene 



OBSERVATIONS WITH THE ZENITH TELESCOPE. 77 



As but tittle materia] for this purpose existed in the case of a con- 



ous system, as 



siderable number of tbe stars employed, a complete re-observation of tbe entire list was 

 kindly undertaken by R. E. Tucker, of tbe Lick Observatory, and that of individual 

 stars at other places; finally in the spring of 1899 an appropriation by the trustees of the 

 Gould fund provided for the employment of a computer, so that now what for present 

 purposes may be regarded as the final values of the stellar coordinates are available. 



In the present series the plan proposed in L 890 by Dr. F. Kustner* was followed. 

 This consists in the employment of lour groups of stars, so arranged that they may be 

 connected by evening observations on one group, accompanied by morning observations 

 on the consecutive one. This furnishes the means of adjusting the results to a homo- 

 geneous system, and at the same time, as a, kind of by-product, a determination of the con- 

 stant of aberration independently of variations in the latitude. 



In the present case the four groups were distributed as follows: 



Group I 5 h 81» to 7"23"' 10 pairs. 



II 14 1 to 15 51 10 " 



III 17 80 to 19 85 9 " 



IV 21 89 to 23 52 12 " 



The interval between 1 and II proved to be somewhat too great, for, although these 

 groups were observed during the long nights of January, February and March, the exces- 

 sive proportion of unfavorable weather at this season made it somewhat difficult to obtain 

 the desired number of satisfactory observations. 



The Instrument. 



This is a Zenith Telescope by E. & G. W. Blunt, of New York- It is said to have 

 been purchased of the United States Coast Survey in 1868, when the Observatory was 

 first erected. It was then in poor condition, and had probably not been in active service 

 for some time. It was at different times overhauled and repaired, and finally, in 1892, 

 provided by (J. Saegmuller, of Washington, with two very line levels. Though not rank- 

 ing as a first-class modern instrument, it proved capable, with care and attention in its 

 use, of giving results which are believed to be worthy of entire confidence. 



The aperture of the telescope is three inches; focal length, forty-one inches. A 



diagonal 



eye-piece was employed, magnifying seventy-five diameters. 



The Levels. 



The two levels above mentioned were designated A and 15. Previous experience with 

 levels had shown that in some cases Urn scale values did not remain constant. Cases of 

 deterioration had also been met with, good tubes in time becoming worthless. 



* Aetronomitche Wachrichten, 13d. 12G, No. 3015. 



