119 



shifting ; and the operation of the arrangement is found to be 

 perfect at all altitudes. 



The construction of the tubes, the piers, the mechanism 

 of the counterpoises, occupied the remainder of this year and 

 the beginning of 1844. In August, a partial polish was given 

 to the mirror in order to verify its focal length (which was 

 found exactly fifty-four feet) ; and the observing galleries and 

 the apparatus for controlling the instrument in right ascension 

 were proceeded with. All these gigantic constructions (of 

 whose prodigious mass some idea may be formed from the fact 

 that they contain, along with their other materials, more than 

 one hundred and fifty tons of iron castings), have been exe- 

 cuted in Lord Rosse's workshops, by persons taken from the 

 surrounding peasantry, who, under his teaching and training, 

 have become accomplished workmen, combining with high 

 skill and intelligence the yet more important requisites of 

 steady habits and good conduct. It may aiso be mentioned 

 that (such was the clear and definite arrangement of the whole 

 in its inventor's mind) nothing failed from first to last ; and it 

 was not necessary for him in any instance to retrace his steps. 



At the beginning of February, 1845, the work being suffi- 

 ciently advanced to permit the use of the instrument without 

 personal danger. Dr. R. and his friend Sir James South were 

 invited to enjoy the trial of it. Its appearance is certainly 

 peculiar, and presents a striking contrast to the more compli- 

 cated framing of the three-feet telescope which is placed beside 

 it. At first sight, one wonders how it is to be moved, for 

 nothing attracts notice except the massive piers and the tube ; 

 but a nearer approach shews that it is the perfection of mecha- 

 nical engineering. To have mounted it on the plan of the 

 three-feet would have been impracticable as well as useless. 

 The speculum with its supports is seven times the weight of 

 that in Herschel's four-feet, and both on this account, and the 

 well-known principle that similar machines are weaker in pro- 

 portion to their bulk, such a stand must have been so heavy 



