AuT. XX. — The New Chain Test Range at the Melbourne 

 Observatory. 



By R. L J. Elleuy, C.M.G., F.R.S., F.R.A.S. 



[Read 14th December. 1893.] 



The old chain test range laid down in the Observatory grounds 

 in March, 1871, was found in January, 1892, to have a small 

 increasing error, and being only six inches above the ground 

 surface, was found inconvenient to use. It was formed by five 

 cubical blocks of sandstone, set on brick and cement foundations, 

 one at either end of the 100 feet range, others at 50 feet, 33 

 feet, and 66 feet. Gun-metal plates fixed to the stones carried 

 the fiducial marks. In March, 1893, a new range was erected, 

 consisting of four heavy brick and cement piers, 2ft. 5in. high, 

 2ft. long, by 18in. wide, capped with blocks of rubbed " blue- 

 stone." A platform from pier to pier was built of stout deal 

 planks, T-shaped, supported on Bin. by 6in. red-gum posts firmly 

 fixed in the ground. The height of this platform and surface of 

 cap-stones is about 2ft. 5in., and very convenient for measuring 

 and comparing. The fiducial marks are on gun-metal blocks, 

 fastened to the stone caps at Oft., 50ft., 66ft., and 100ft. On 

 the 66ft. pier are two marks 12in. apart ; one is 16ft. from the 

 50ft., and the second 33ft. from the 100ft., so as to obtain a 

 standard foot and a half-chain measure. At the terminal piers 

 wooden pillars are fixed to hold the adjusting screws and tension 

 springs for stretching chains and tapes, and the fiducial marks 

 are arranged to measure from end handles ("but a but ") or 

 marks (" traits "). Tension can be given to any chain, tape, or 

 other measure at any intermediate point by means of a shifting 

 toggle, to which the tension screws can be attached. The measures 

 of this range wore made with the 10ft. steel bars used for the 

 A'ictoriaft. base line, the measurement being made in the same 

 manner — that is, bars placed end to end, but about one-fourth of 

 an inch apart, aligned and levelled, the space being measured 



