The Sun.
London, England, 1842-05-09 00:00:00

THE EARL OF ROSSE'S
TELESCOPE.

- The subjoined account of the Earl of Rosse's noble
Telescope, now casting and in formation, is from the
pen of Sir James South, the eminent astronomer :
The foundry is not many feet from Birr Castle, the
residence in Ireland of the Earl of Rosse, and, with
the exception, of the crucibles, which were made by
Messrs. Dewer, of Old-street, St. Luke's, all the ap-
paratus employed on this interesting occasion (the
steam-engine itself included) was made in workshops
adjoining the Castle, under the Earl's immediate di-
rections, by workmen trained and instructed by him-
self.

The casting of the speculum of this leviathan
telescope having been safely effected, I forward a
brief description of the modus operandi adopted by the-
Noble Earl, in the confidence that by very many of
your intellectual readers it will be gratefully received
both at home and abroad.

As, however, diagrams are not well suited to news-
paper columns, I must endeavour to provide a substitute.
Make, then, one extremity of a line 41 inches long
bisect a perpendicular to itself of 24- inches long, and
the other extremity of it bisect another perpendicular
to itself of 2 inches and 3 tenths ; beyond which per-
pendicular extend the first-named line 2i inches.
Call the first, the crane line ; the second, the chim-
ney line; and the.third, the mould line.
On the crane line, at the distances from the chimney
line of 1 inch and 2 tenths, 2 inches and 4 tenths, and
3 inches and 6 tenths; make dots. On the first of
these dots place, centrally, a silver fourpence ; on the
second, a silver penny ; on the third, a sixpence ; on
the centre of the chimney line, a shilling ; on each of
its extreme points, a silver fourpence ; on the centre
of the mould line, a crown ; on each of its extreme
points, a sixpence ; and on the uncovered extremity
of the crane line, a card of 2 inches square, so that
its extremities shall lie parallel with or perpendicular 1
to the crane line.

Now, supposing these several coins and card to have
the same' thickness as the silver fourpences, the toad
ensemble will indicate an horizontal section of the
foundry; for the three fourpences will represent the
crucibles in their furnaces, the shilling the chimney,
the penny the crane, the crown the bottom of the
mould, the sixpences the iron pouring baskets, and the
card the floor of the annealing oven.
The crucibles were of cast-iron, 24 inches interior
diameter, and 30 inches deep, each weighing abOut
half a ton. They were kept in situ above the bars of
the furnaces by cast-iron supports and subjacent
brickwork.

The furnaces, about 5,} het square, were brick ;
their fuel apertures were 4 feet diameter ; their height
above the gratings, 8 feet ; their ashpits, 2 feet ; and
their several flues passed into the chimney, which was
54- feet square at bottom, and in height was many yards.
The iron pouring-baskets were supported on wooden
frames, and were supplied with pivots ; one pivot of
each basket having had welded on it at a convenient
angle an iron lever about three feet long, by which
fee basket, with its contents, was turned on the pivot
of the former without difficulty.
The bottom of the mould, 6 feet 8 inches in dia-
meter, was formed of iron hoops 6 inches broad,
packed as closely as possible side by side, their edges
up, and turned in the lathe till the upper surface had
imparted to it a convexity necessary to produce the
wished-for concavity in the surface of the speculum
when east.

A half-crown placed centrally on the crown-piece
will represent the wooden pattern for the mould ; it
was full 6 feet diameter, and' about 5/ inches thick.
The bottom of the mould (the crown-piece) was now
included in a quadrangular wood frame, and sand
being crammed. between it and the wooden pattern,
the latter was removed with the crane, and the mould
thus made, being so perfectly horizontal, was ready
to receive the melted mass.
The metals of which the speculum is composed ,are
copper and tin, 126 parts of the former to <';7).:, of the
latter; had it been 58" of tin, the proportions would
have been the atomic Otinclard. .

..•, q,'. ,u. y.

The copper employed was fragments of copper
sheathing, and about three tons of it were used ; the
tin was grain tin. The price of the former is about
1001. a ton, that of the latter I do not know.
At two o'clock in the morning of Wednesday, the
13th instant, the furnaces were lighted, and in about
ten hours the crucibles were in a state fit for receiving
their respective charges.
The metal, which had been previously fused and
broken up, was distributed equally amongst the cru-
cibles, so that any accidental difference in it was pro-
bably destroyed.
By nine in the evening the furnaces were opened,
and the flames of nearly homogeneous yellow light
which issued from them were splendid. The coun-
tenances of the bystanders looked like those of ghosts,
whilst the scarlet coats of the officers present seemed a
dirty yellow.
Tackle from the crane was now fastened to one of
the crucibles at the extremity of the chimney line,
and when raised above its surface, the revolution of
the crane on its centre deposited it as quietly as pos-
sible in its corresponding iron basket; it did the same
for the second crucible, and also for the third.
By turning the iron baskets on their pivots, the con-
tents of the crucibles were simultaneously poured into
the mould, and some minutes elapsed before the un-
dulatory motion of the fluid metal ceased.
In about twenty minutes the quadrangular wooden
frame and sand were removed ; an iron ring con-
nected with a bar passing through the oven at
the back aperture was clamped round the red
hot speculum, the tackle of a capstan was hooked
to the bar, and the speculum was hauled from the
bottom of the mould over an iron railway into the
annealing oven. The oven, whose interior had been
kept at a dull red heat for some days, was now charged
with charcoal, the arches below with turf, and every
opening of the oven built up and plastered over, and
it is supposed that two months will elapse before the
speculum is cool enough to be removed with safety.
Not an accident or anything untoward happened
during the process, and in 40 minutes from the time
of the first crucible being moved the speculum was
safely in the oven.
The metal is 6 feet diameter, it is 51 inches thick at
the edges, and 5 inches at the centre; its weight is
about 3 tons.

By grinding and polishing its thickness will pro-
bably be reduced 1-10th or
,nth of an inch—it will be.
formed into a telescope of 50 feet focal length, and
will, there is every reason to hope, be actually in use
this year.
The speculum will have a reflecting surface of
4,071 squaxe inches, whilst that of the telescope made
bv the immortal Herschel, under the auspices of King
George 111. had but 1,811."