The eye-pieces adapted to this telescope have powers which magnify the object linearly from 100 to 1500 times, which are competent to fulfil all the purposes of vision when cleared of aberration. When the telescope is placed in the plane of the meridian and elevated together with the gallery, into any required altitude, the _meridional sweeps_, formerly practised by Sir W. Herschel, and continued by Sir John with great success, in the examination of double stars and nebula, may be managed with great ease.
Mr. Ramage had a telescope of about the same size, erected in an open space in Aberdeen, which I had an opportunity of inspecting when I paid a visit to that gentleman in 1833; but cloudy weather prevented my obtaining a view of any celestial bodies through it. He showed me at that time two or three large speculums, from 12 to 18 inches in diameter, which he had finished some time before, and which appeared most beautifully polished. He told me, too, that he had ground and polished them simply with his hand, without the aid of any machinery or mechanical power--a circumstance which, he said, astonished the opticians of London, when it was stated, and which they considered as almost incredible. His experience in casting and polishing metals of various sizes, during a period of 15 or 16 years, qualified him to prepare specula of great lustre, and with an unusually high polish. It has been asserted that a fifty feet telescope by Ramage of 21 inches aperture was intended to be substituted for the 25 feet instrument erected at Greenwich, and the speculum it is understood, was prepared, and ready for use, provided the Navy Board was disposed to defray the expense of carrying the plan into execution. But, unfortunately, this ingenious artist was unexpectedly cut off in the midst of his career, about the year 1835.
SECT. 4.--THE AERIAL REFLECTOR--CONSTRUCTED BY THE AUTHOR.
A particular description of this telescope was given in the ‘Edinburgh New Philosophical Journal’ for April--July, 1826, conducted by Professor Jameson, the greater part of which was copied in the ‘London Encyclopedia,’ ] under the article _Telescope_. From this description I shall endeavour to condense a brief account of this instrument with a few additional remarks.