204 abstracts: astronomy 



error, the magnitude of which has been considerably reduced at the Ob- 

 servatory. 



When the telescope is above the pier the thrust of the declination spin- 

 dle is taken up by ball bearings, but when below the weight comes against 

 a tool-steel collar evidently not intended to support it. It is clear that 

 the designer did not quite comprehend how the instrument was to be 

 used, since in the case of many objects in the south it is necessary to 

 observe with the telescope under the pier. 



When the 26-inch instrument left the makers the arrangement for 

 illuminating the declination circle was not altogether satisfactory, and 

 the circle could not be properly utilized. The illumination has been 

 improved somewhat. 



Three micrometers have been employed with the large Equatorial: 

 Clark Micrometer I, Clark Micrometer II, and that by Warner and 

 Swasey. The last has not been of much use. All these instruments 

 have excellent screws, but were all constructed by men who were not 

 quite familiar with the measurements that had to be made with them, 

 and about the necessity for avoiding systematic errors, and they all have 

 unnecessary defects. 



In 1904 a bright field illumination was arranged by reflecting light 

 from a small 2 candle power lamp to the inner surface of the objective 

 by means of a prism within the telescope tube near the eye-end and just 

 outside the cone of rays. A good illumination is furnished for magni- 

 fying powers up to about 550. 



In the selection of work for the equatorial instruments the usual policy 

 of the Naval Observatory has been followed, that observations should 

 for the most part be for the improvement of the places of the Sun, 

 Moon, and planets, and the fixed stars, and for the testing of the laws 

 according to which the heavenly bodies are supposed to move. Usually, 

 also, heavy pieces of observing are taken up which would not be cared 

 for elsewhere, which it is necessary to extend over considerable periods, 

 and in which it is important to secure continuity. 



The plan of work, therefore, was to observe, (1) the satellites and the 

 diameters of planets, (2) some of the interesting and difficult double 

 stars, (3) minor planets and comets, and (4) occultations of stars by the 

 Moon. The 26-inch has been devoted to the fainter and more difficult 

 objects. Continuity in the observations of the satellites of Saturn, 

 Uranus, and Neptune was considered important. 



For about two years, 1898-1900, attempts were made to do spectro- 

 scopic work with the 26-inch Equatorial, in the way of determining 



