96 Things not generally Known. 



selves, may remember its extraordinary aspect when seen from the 

 Bath coach-road, and the road to Windsor. The difficulty of managing 

 so large an instrument requiring as it did two assistants in addition 

 to the observer himself and the person employed to note the time 

 prevented its being much used. Sir John Herschel, in a letter to Mr. 

 Weld, states the entire cost of its construction, 400CM., was defrayed by 

 George III. In 1839, the woodwork of the telescope being decayed, 

 Sir John Herschel had it cleared away ; and piers were erected, on 

 which the tube was placed, that being of iron, and so well preserved 

 that, although not more than one-twentieth of an inch thick, when in 

 the horizontal position it contained within all Sir John's family ; and 

 next the two reflectors, the polishing apparatus, and portions" of the 

 machinery, to the amount of a great many tons. Sir John attributes 

 this great strength and resistance to the internal structure of the tube, 

 very similar to that patented under the name of corrugated iron-roping. 

 Sir John Herschel also thinks that system of triangular arrangement 

 of the woodwork was upon the principle to which " diagonal bracing" 

 owes its strength. 



THE EARL OF ROSSE's GREAT REFLECTING TELESCOPE. 



Sir David Brewster has remarked, that " the long interval 

 of half a century seems to be the period of hibernation during 

 which the telescopic mind rests from its labours in order to ac- 

 quire strength for some great achievement. Fifty years elapsed 

 between the dwarf telescope of Newton and the large instru- 

 ments of Hadley ; other fifty years rolled on before Sir William 

 Herschel constructed his magnificent telescope ; and fifty years 

 more passed away before the Earl of Rosse produced that colos- 

 sal instrument which has already achieved such brilliant disco- 

 veries." * 



In the improvement of the Reflecting Telescope, the first 

 object has always been to increase the magnifying power and 

 light by the construction of as large a mirror as possible ; and 

 to this point Lord Rosse's attention was directed as early as 

 1828, the field of operation being at his lordship's seat, Birr 

 Castle at Parsonstown, about fifty miles west of Dublin. For 

 this high branch of scientific inquiry Lord Rosse was well fitted 

 by a rare combination of " talent to devise, patience to bear 

 disappointment, perseverance, profound mathematical know- 

 ledge, mechanical skill, and uninterrupted leisure from other 

 pursuits ;"f all these, however, would not have been sufficient, 

 had not a great command of money been added ; the gigantic 

 telescope we are about to describe having cost certainly not 

 less than twelve thousand pounds. 



Lord Rosse ground and polished specula fifteen inches, two feet, and 

 three feet in diameter before he commenced the colossal instrument. It 

 is impossible here to detail the admirable contrivances and processes by 

 which he prepared himself for this great work. He first ascertained 



* Life of Sir Isaac Nfwton, vol. i. p. 62. 



| Description of the Monster Telescope,, by Thomas Woods. M.D. 4th edit. 1851. 



