On the Cork Equatorial Telescope, &c. 363 
The Instrument consists of a cast iron frame supporting a 
4-inch achromatic telescope pointing directly at the south pole of 
the earth. Below the objective, and in line with it is supported 
a mirror polished with the greatest care to an optically plane 
surface, and silvered with a coating of chemically deposited silver. 
The telescope revolves on its own axis either by hand or by 
clockwork as required, and this motion corresponds to the ® 
movement of an equatorial. The mirror has a motion on its axis, 
and this corresponds to the declination movements of an equa- 
torial. 
The whole framing is carried, when not vi use, on four rollers, 
rolling on a pair of iron rails let into the floor. When required 
for use the instrument is rolled over to a window specially pre- 
pared for it in the south wall of the Physical Wing, the lower 
part of this window opens, and the instrument is rolled out until 
the mirror, objective and a certain portion of the tube projects 
outside the building, while the eye-piece remains in a conveni- 
ent position inside. The wheel (W), see Fig. 10, is now turned, 
and the whole frame is lowered down until three levelling screws 
come to bear on three cushions of iron specially prepared for 
them, and let into a solid stone pier just projecting through, but 
quite disconnected from, the floor of the room. The instrument is 
now in a condition for observing, supported on a solid stone pier, 
and with its object glass in the open air under most favourable 
conditions for observation, while the observer is situated most 
comfortably, and perfectly sheltered inside the observatory. It 
‘should be borne in mind that as there is in this case no open 
window, or, indeed, any opening in the wall (as the frame is so 
so constructed as practically to keep out draughts), the telescope 
is not under the unfavourable condition that it would be if 
simply placed at an open window where the currents of differing 
temperatures just meet and mix. All objects from zenith to 
south horizon, and from E. to W. are now available for observa- 
tion. 
For setting the instrument there is a A circle divided to 2 m., 
and reading to 10 sec., at the upper end of the tube, and there is 
a declination are on the mirror frame read by the microscope 
from the eye-piece end, and by a peculiar arrangement this micro- 
scope also serves for illuminating the declination are. 
