July 21, 1923] 



NA TURE 



105 



made provision in his estimates for the erection of a 

 visual refractor of 26 inches clear aperture, and a 

 contract with 5ir Howard Grubb and Sons, Ltd. was 

 signed in November of that year. Discs for the 

 objective were ordered at once from France, but the 

 production of optical glass of that size is a slow and 

 uncertain process, and in 191 2 efforts were made to 

 obtain a supply from Messrs. Chance Bros, and Co., 

 Ltd., of Smethwick, near Birmingham. 



Trials and disappointments followed, parallel and in 

 series too. At this time Sir David Gill, the designer 

 of the telescope, had inspected the equatorial and 

 reported " Nearly complete and exceedingly satis- 

 factory " — this was in the summer of 191 2. There 

 followed two years full of hope passed in fresh efforts 

 and experiments. Then the Great War put a stop to 

 everything. , . . The Armistice came at last, and when 

 the smoke of battle cleared away it was found that the 

 Admiralty had silently transferred Sir Howard Grubb's 

 workshops from Rathmines, near Dublin, to St. 

 Albans, and there in the confused heaps of material, 

 tools, patterns, periscopes, range-finders, and waste, 

 lying on the new workshop floors, it was said the 

 famous telescope was lying dismembered and for the 

 most part unrecognisable. 



It was necessary to start again, not quite from the 

 beginning but very nearly so, and this necessitated con- 

 ferences, new estimates, and references to Pretoria, but 

 finally order arose out of chaos. Fresh contracts were 

 made in November 1922, and in the following March 

 Messrs. Chance Bros, reported complete success. 

 On their invitation a few astronomers journeyed to 

 Birmingham to view these long-desired discs, and there 

 the visitors experienced moments, nay minutes of 

 tension. The room containing this precious optical 

 glass proved unsuitable for the examination, so two 

 workmen carried the flint disc weighing some 240 lbs. 

 in their four bare hands through a narrow doorway 

 across an uneven floor, wending their way between 

 great blocks of glass into another room. Perhaps it 

 was not as dangerous as it looked, but to the interested 

 spectators it seemed a passage perilous, where the 

 labour of thirteen years might have been lost by an 

 unlucky step. 



These two discs, when tested for striae and annealing, 

 satisfied the optical expert, and they were taken to 

 St. Albans, where the rough grinding of the flint is 

 proceeding as shown in Fig. i. To the objective it is 

 intended to give the form now generally familiar to 

 astronomers : a double convex crown fronts the stars 

 and is followed at a distance of some six inches by a 

 double concave flint, the fourth surface being of 

 extremely long radius. In its mounting a close-fitting 

 sliding band will make it possible to clean either or 

 both the inner surfaces, and here it has been essential 

 to pay special attention to the complete exclusion of 

 dust, of which Johannesburg easily obtains its share. 

 The rough discs measured 26J inches, and are to yield 

 a finished objective of 26 inches clear, with a focal 

 length of, say, 35 feet, giving a ratio just over 16. 



The dome for the telescope has been ready and in 

 position for so long that its appearance in any photo- 

 graph of the outskirts of Johannesburg must be quite 

 familiar to many. A good photograph of the whole 

 instrument on its equatorial as it stands in Fleet Works, 



NO. 2803, VOL. II2J 



St. Albans, cannot be obtained, and yet it is probably 

 the most frequently photographed telescope in the 

 eastern hemisphere ; since Christmas last, views of it 

 have appeared in two of London's leading newspapers, 

 but each time it has been ascribed to Russia, and on the 

 first occasion it was even described as the largest 

 telescope in the world. 



Fig. 2 shows the view from the south-west of the 

 heavy castings for the stand with the polar axis carry- 

 ing the right ascension circle at its lower (north) end. 

 Most of the tube is visible, with its central cube and the 

 extension for the counterpoise. Fig. 3 is the breech- 

 piece with photographic plate-holder. It shows also 

 the 4-inch finder of 60 inches focal length. This is 



Fig. I. — Flint disc. 



provided with either a variable bright field or with 

 bright wires as desired for the particular work in hand. 

 Several of the circular weights are to be seen the 

 removal of which will make it possible to fit a spectro- 

 graph if it is so desired at any time in the future. These 

 weights equal in all 370 lbs. The motive power for 

 the driving clock is a weight which falls a quarter of 

 an inch every ten seconds — the rewinding is automatic 

 and electric. The weight of the moving parts amounts 

 to more than five tons, but the roller bearings supplied 

 and the carefully equal distribution of the mass make 

 it easy for the observer to shift this load with one hand. 

 The process of finding a faint star with this instru- 

 ment is not quite as ordinarily obtains — it is more 

 simple. The declination clamp is released, and the 

 required declination reading is obtained ; the instru- 

 ment is then re-clamped. Now, because the right 

 ascension circle is clock-driven, it constantly indicates 



