WITH A FOURTEEN FEET REFLECTOR. 167 



under more favourable circumstances, by observers of greater skill and longer 

 practice. 



3. The observations presented in the following paper are a portion of a series 

 undertaken in the summer of 1839. The range of objects which at that time 

 passed under inspection was considerably more extensive than the present list; 

 but many of these were examined in a desultory manner, and the rest of those 

 excluded are not favourable specimens of the style of observation M'hich it is 

 intended to exemplify. The telescope employed was of the Herschelian con- 

 struction, with an aperture of twelve inches and a focal length of fourteen feet. 

 A short description of its construction and powers will not be uninteresting, 

 and may serve to show what degree of confidence is warranted in results ob- 

 tained by its aid. Although much inferior in size and light to some of the 

 gigantic reflectors of the Herschels, it yet is entitled to some distinction as the 

 largest telescope on this side of the Atlantic. The instrument was first planned 

 and begun in the summer of 1838, by my friend and classmate, Mr. H. L. 

 Smith. A tolerably good metal was cast, after several failures, and the specu- 

 lum was finally polished near the close of the summer. Mr. Smith and Mr. 

 Bradley shared the expenses attending the formation of the mirror and erection 

 of the telescope, and divided the long labour of grinding the speculum, and I 

 united with them in the less tedious task of giving the mirror its final polish 

 and figure. An account of its performance in some of our first rough trials of 

 its figure is furnished in a note on the 174th page of the XXXVth volume of 

 Silliman's American Journal of Science. It has since been frequently and 

 perseveringly repolished by Messrs. Smith and Bradley; the test objects men- 

 tioned in that note, however, have been about the limit of its separating power. 



4. The mode of mounting the telescope was similar to Ramage's, but ruder. 

 The base consisted of three beams, forming a triangle, which revolved on a 

 circular ledge of plank, by means of rollers at the angles, and which was 

 guided truly in its circuit by a cross-piece, through which rose a central bolt, 

 firmly driven into the ground. From the angles of this base rose three beams, 

 meeting at a height of sixteen or seventeen feet from the ground, and a rope 

 passed through a pulley fixed at this height, and sustained the weight of the 

 upper part of the telescope. The lower end, containing the speculum, rested 

 on a small platform at one of the solid angles of the base, and revolved with 

 the frame. The quick motion in altitude was by means of the rope just men- 



