AN ACCOUNT 



OF 



THE CONSTRUCTION AND USE OF A SILVERED GLASS TELESCOPE. 



The construction of a reflecting telescope capable of showing every celestial 

 object now known, is not a very diificult task. It demands principally perse- 

 verance and careful observation of minutise. The cost of materials is but trifling 

 compared with the result obtained, and I can see no reason why silvered glass 

 instruments should not come into general use among amateurs. The future hopes 

 of Astronomy lie in the multitude of observers, and in the concentration of the 

 action of many minds. If what is written here should aid in the advance of that 

 noble study, I shall feel amply repaid for my labor. 



A short historical sketch of this telescope may not be uninteresting. In the sum- 

 mer of 1857, 1 visited Lord Eosse's great reflector, at Parsonstown, and, in addition 

 to an inspection of the machinery for grinding and polishing, had an opportunity 

 of seeing several celestial objects through it. On returning home, in 1858, I 

 determined to construct a similar, though smaller instrument; which, however, 

 should be larger than any in America, and be especially adapted for photography. 

 Accordingly, in September of that year, a 15 inch speculum was cast, and a 

 machine to work it made. In 1860, the observatory was built, by the village 

 carpenter, from my owa designs, at my father's country seat, and the telescope 

 with its metal speculum mounted. This latter was, however, soon after abandoned, 

 and sUvered glass adopted. During 1861, the difliculties of grinding and polishing 

 that are detailed in this account were met with, and the remedies for many of them 

 ascertained. The experiments were conducted by the aid of three 15g inch disks 

 of glass, together with a variety of smaller pieces. Three mirrors of the same 

 focal length and aperture are almost essential, for it not infrequently happens that 

 two in succession will be so similar, that a third is required for attempting an 

 advance beyond them. One of these was made to acquire a parabolic figure, and 

 bore a power of 1,000. The winter was devoted to perfecting the art of silvering, 

 and to the study of special photographic processes. A large portion of 1862 

 was spent with a regiment in a campaign in Virginia, and but few photographs 

 were produced till autumn, when sand clocks and clepsydras of several kinds having 

 been made, the driving mechanism attained great excellence. During the winter, 

 the art of local corrections was acquired, and two 15| inch mirrors, as well as two 

 of 9 inches for the photographic enlarging apparatus, were completed. The greater 

 part of 1863 has been occupied by lunar and planetary photography, and the 

 enlargement of the small negatives obtained at the focus of the great reflector. 

 Lunar negatives have been produced which have been magnified to 3 feet in 



1 May, 1864. ( 1 ) 



