408 Dr. Herschei/s Description of a 
object be to put its own cover upon it before any thing be 
done about fixing it there. 
In very high observations the tube will not fall down again 
readily, and in the zenith, by its great weight added to that 
of the mirror, will even tilt backwards. A counterpoise there- 
fore is applied by a meridional post, 7 feet high, well fastened 
by a frame in the ground ; and placed about 20 yards from 
the front of the telescope. To this is fastened at the top on 
the back an arm, which carries a pulley, and at the bottom on 
the front, a barrel moved by a wheel and pinion. A rope with 
a weight fastened to the end of it, goes over the pulley on the 
post, and towards the mouth of the telescope. At the end of 
the tube on each side is a loop, into which a chain is hung 
with both ends. It is long enough to go round the seat to a 
considerable distance, and holds a pulley in the middle, over 
which the rope from the weight is made to pass back again to 
the barrel at the post. Here it may be drawn up till the 
weight is lifted sufficiently to keep the telescope steady, and 
to make it fall again, when its own motions lower it. In ze- 
nith sweeps 300 weight are required for that purpose, but one 
hundred of that quantity is in shifters that may be taken off 
in lower altitudes, when less is sufficient. 
A similar post and apparatus is fixed about the same dis- 
tance from the telescope towards the north, to be used when 
the instrument is turned about for high observations in the 
northern meridian. 
Another inconvenience to be removed in very high alti- 
tudes, is that the long bars, which bring the point of support 
forwards, begin to project beyond their supporters. When this 
