166 PROCEEDINGS OF THE AMERICAN ACADEMY 



The declination-circle is two feet in diameter, and reads by four ver- 

 niers to four seconds in arc. The object-glass has fifteen inches clear 

 aperture, and twenty-two feet eight inches focus. It is furnished with a 

 filar-position micrometer, and four annular micrometers. There are 

 eighteen eye-pieces, the highest power being estimated by the maker 

 at two thousand. After adjusting and securing the various parts, the 

 whole was found to move freely and steadily under clock-work, it 

 being well balanced in all its parts, and the friction greatly reduced, 

 by a judicious arrangement of counterpoises and friction-wheels. The 

 instrument is protected from the weather by a dome of thirty feet in- 

 terior diameter. It moves freely on eight cannon-balls, and is secured 

 from displacement by storms, by eight iron braces, which are secured 

 to the walls of the building, and present friction- wheels to the opposite 

 sides of the interior of the dome. The opening is five feet wide ; the 

 shutters are opened and closed by means of endless chains, working in 

 teethed pulleys turned by a crank. I omit the details of mounting 

 the telescope, as they are of little general interest, and will be given 

 in the report to the Visiting Committee on the Observatory, when I 

 hope to be enabled to add to them an account of the new transit- 

 circle, which Mr. Simms has nearly completed, 



" In regard to the ultimate capabilities of our telescope, we cannot 

 be expected, from so short a trial, to have formed any very decisive 

 opinion. It has, however, even under the disadvantage of a bad state 

 of the atmosphere, exceeded our expectations. We have had the best 

 opportunities of making observations during the early morning hours. 



" Of the close double stars, our attention was first directed to tj Co- 

 ronse. The components appeared round, small, and well separated. 

 The difficult double star y Coronae, which Captain Smyth ranks 

 in his ' Cycle ' as the ' Praeses of Struve's vicinissimae,' was well 

 separated, a dark space appearing between the principal star and its 

 satellite. On the morning of the 20th July, the companion of/ An- 

 dromedse was also well separated. The line micrometer gave a dis- 

 tance of three tenths of a second. I was surprised to find, on following 

 this object into day-light, that our measures of distance could be taken 

 after sunrise. I measured, alternately with my son, both in distance 

 and position, while the sun was shining on the telescope, and we both 

 thought that we saw them full as well, or rather better, after sunrise 

 than before. This might be owing to a quieter state of the atmos- 

 phere consequent on a rise of the thermometer. On the evening of 

 the 15th of July, the nebula No. 27 Messier, commonly known as 



