THE GEEAT MELBOUENE TELESCOPE. 
147 
part is lattice-work made of slips of steel ^ inch thick, 3 inches broad at bottom, and 
tapering to 1-J at top. These were bent round a cylinder of the proper diameter, as 
shown in Plate XII. fig. 15, and each crossing was secured by a rivet, forming a series of 
lozenges about 9 by 17 inches. Strong iron rings were rivetted to each end, the lower 
of which was secured to the close part; and four strong diaphragms were similarly 
attached at equal distances in its interior. The open part is 21 feet long. As a proof 
of its exceeding stiffness, may be mentioned that a weight of 112 lbs. hung at its extre- 
mity only caused a deflection of inch. The small speculum is carried by a steel arm 
of considerable depth attached to the second diaphragm, which is of steel, and supported 
by struts from the first and third. Provision was made for transverse support, but this 
has not been found necessary. 
[Plate VI. fig. 16 is an end elevation, and Plate V. fig. 17 a side elevation of the small 
speculum in its box, and apparatus for carrying and adjusting it ; scale 1^ inch to the foot. 
A cast-iron plate a, 18 inches long, is attached to the inside of the tube, at one end 
by a small cross girder b, and at the other by a lunette steel ring c (fig. 16). To this is 
attached, by two thumb-screws, the plate d (fig. 17), forming the base of the hollow arm 
A, which is made of steel plate -j 3 ^ inch thick, and filled with wood to deaden the vibra- 
tion. This carries at its upper end a V-shaped gun-metal slide B, in which works the 
arm e, to which the speculum-box is attached by three screws,/ 1 , /’. Between the plate 
which forms the end of the arm and the speculum-box are two rings, g, g, of a greater 
thickness at one side than the other, by the relative revolutions of which the speculum 
is adjusted at right angles to the axis of the large speculum. For focusing the arm e 
is acted upon from behind by a screw, to which motion is given by the wire cords h. 
These cords are carried over the pulleys b and down the side of the tube to its lower 
end, where they are wound round a hand- wheel concentric with the eyepiece, to which 
motion can be given by the observer for the purpose of focusing (see next fig.). 
Plate VI. fig. 18 is apian of the bottom of the speculum-box, which forms the lower 
end of the telescope, showing the arrangements for hand motions, &c. ; scale 1^ inch to 
the foot. 
a, a are two of the three bolts by which the speculum-box is attached to the end of the 
tube ; b, b, b the three screws for levelling the speculum : these screws form the support 
of the three primary levers already described ; their heads are countersunk in the bosses, 
and are covered when not in use by brass caps. A is the lowest eyepiece, power 220 ; 
field-lens 8 inches diameter ; c is the hand-wheel for focusing ; the cords h, h from this 
are carried up the side of the tube to the apparatus already described (Plate VI. fig. 16 
& Plate V. fig. 17). B is the hand-wheel for quick motion in declination. The motion is 
obtained by a pinion on the upper end of the shaft of the wheel d, gearing into a toothed 
wheel 4 feet 6 inches diameter, attached to the cube of the polar axis, as seen at S in fig. 15. 
C is the wheel for slow motion in declination. This is obtained by a clamp (S, fig. 15) 
4 feet 6 inches diameter, with a tangent screw and parallel motion similar to that after- 
wards to be described for Al, and D is the HooK’s-joint handles for the apparatus as 
