448 Description of the Great Southern Telescope. [ Oct., 
their box on Mr. Grubb’s system of hoops; the whole system 
of suspension and levers, presently to be described, weighs alto- 
gether nearly 2 tons. 
Of the tube, 7 feet is made of boiler-plate iron, quarter inch 
thick, to which is attached by flanges and bolts a skeleton tube, 
21 feet long, of steel bars, 3 inches wide at bottom, 14 at top, and 
1 of an inch thick, wound spirally round rings of carefully turned 
angle iron and riveted at the joints, forming a spiral lattice of 
amazing strength, stiffness, and freedom from tremor. The 7 feet 
‘of boiler-plate tube weigh 1,300 lbs., and the 21 feet of the 
ventilated tube only 1,370 Ibs. 
At the upper end of the tube, about 25 feet 6 inches from the 
large mirror, is bolted a very stiff hollow arm of steel-plate, on 
the extremity of which is a V-shaped gun-metal casting, i which 
slides an arm carrying the small mirror of 8 inches diameter. 
This arm is acted upon from behind by a screw, from a pulley on 
the shaft of which wire-cords are carried over iron guide-wheels 
down the side of the tube, where they are wound round a wheel to 
which motion can be given by the observer, for the purpose of 
focussing. 
The polar awis is made up of four distinct parts, vz. a cube 
3 feet square, to which is bolted on one side a cone 8 feet long 
which terminates with a bearing 12 inches diameter, resting in a 
peculiar “plumber-block” on the polar pier, on the opposite side 
a short toe-piece, which carries on parts prepared for them the two 
hour circles, sector, and clamp, and terminates in a bearing 6 inches 
diameter resting in a Y block in the equatorial pier, and on a third 
side a bell-shaped casting about 2 feet long, which terminates in a 
slide carrying one bearing of the declination axis, the other being 
in the side of the cube opposite the bell. 
The declination axis is 24 inches diameter at the bearing next 
the telescope, and 12 inches at the other, the bearings being 5 feet 
asunder and the axis itself about 9 feet long. It carries at one end 
the telescope strapped into its cradle, and at the other counterpoise 
weights, amounting to over 2 tons. 
The counterporse weights are four circular cast-iron boxes, con- 
sisting of a ring 10 inches diameter. which is bored out to fit the 
axis, and an outer ring 30 inches diameter, both 6 inches deep, 
connected by a plate to form a bottom, and divided into six segments 
by ribs. These chambers are mostly filled with lead, the outer one 
being left with a little spare space for adjustments. 
The bearings of the polar aais, on the principle of Ys, are 
constructed with as much delicacy and care as those of a theodolite. 
The upper bearing, 12 inches diameter, consists essentially of 
a large “ plumber-block,” in which slide, in horizontal grooves, two 
