THE CASTLE, PARSONSTOWN,
_1848, Aug. 30_.

Yesterday we were employed entirely about the Great Telescope,
beginning rather late. The principal objects had relation to the fault
of definition when the telescope is pointed low (which I had remarked
on the preceding night), and were, to make ourselves acquainted with
the mechanism of the mirror's mounting generally, and to measure in
various ways whether the mirror actually does shift its place when the
telescope is set to different angles of elevation. For the latter we
found that the mirror actually does tilt 1/4 of an inch when the tube
points low. This of itself will not account for the fault but it
indicates that the lower part is held fast in a way that may cause a
strain which would produce the fault. These operations and reasonings
took a good deal of time. Lord Rosse is disposed to make an alteration
in the mounting for the purpose of correcting this possible strain.

THE CASTLE, PARSONSTOWN,
_1848, Aug. 31_.

The weather here is still vexatious: but not absolutely repulsive.
Yesterday morning Lord Rosse arranged a new method of suspending the
great mirror, so as to take its edgewise pressure in a manner that
allowed the springy supports of its flat back to act. This employed
his workmen all day, so that the proposed finish of polishing the new
mirror could not go on. I took one Camera Lucida sketch of the
instrument in the morning, dodging the heavy showers as well as I
could; then, as the afternoon was extremely fine, I took another, with
my head almost roasted by the sun. This last view is extremely pretty
and characteristic, embracing parts of the mounting not shewn well in
the others, and also shewing the Castle, the Observatory, and the
3-feet telescope. The night promised exceedingly well: but when we got
actually to the telescope it began to cloud and at length became
hopeless. However I saw that the fault which I had remarked on the two
preceding nights was gone. There is now a slight exhibition of another
fault to a much smaller extent. We shall probably be looking at the
telescope to-day in reference to it.

THE CASTLE, PARSONSTOWN,
_1848, Sept. 1_.

Yesterday we made s