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as to present great obstacles to its motion. The vast surface 
exposed to the action of wind must have made it unsteady ; 
and its durability could not be great. Lord Rosse, therefore, 
determined to confine the range of observation to the vicinity 
of the meridian. There the stars are at their greatest altitudes, 
and atmospheric influences affect them least ; their places can 
be determined with most accuracy, and an equatorial move- 
ment, so essential to micrometer measures, can be easily 
obtained. With such optical power there will never be a 
scarcity of objects for examination; and the restriction will 
only be felt in the case of planetary bodies. The base of the 
actual mounting is a very massive joint of cast iron; its lower 
axis permitting motion in the meridian plane, its upper ina di- 
rection perpendicular to that circle. On this is firmly bolted a 
cubical wooden chamber, about eight feet wide, in which the 
speculum is placed, one of its sides opening for thepurpose. This 
again carries the tube, which when vertical and viewed from the 
interior of the chamber, is more like one of the old round towers 
than any more ordinary object of comparison. It is fifty feet 
long, eight feet in diameter in the middle, but tapering to seven 
at the extremities: it is made of deal staves an inch thick, 
hooped with strong iron clamp-rings, and secured from collapse 
by iron diaphragms ; and carrying at its upper extremity the 
apparatus of the Newtonian small mirror, which, from its great 
weight and bulk requires to be counterpoised, The telescope 
is moved in declination by a strong chain cable attached to its 
top and passing over a pulley fixed at a proper height to the 
north, down toa windlass on the ground which is wrought by 
two workmen. East and west, near the top of the piers, large 
iron pulleys are fixed, having free movement in azimuth, so 
that their planes may always be in those of the traction: chains 
suspending the counterpoise weights pass over these to the 
sides of the tube. The weights, however, are constrained to 
descend in quadrants of circles*by chain guys attached to the 
frame which bears the declination pulley. It is easily seen 
