Burlington free press. [volume] (Burlington, Vt.) 1827-1865, 1847-04-23

means the iron conducted the heat away thro'
the bottom. so as to cool the metal towards the
top while the iutcrstices between the hoops
tho close enough to prevent the metal from run.
ming out were sufficiently open to allow the air
to escape, At nv visit I had an opportunity of
seeing this singular mould; il was large disk
of naable iron, the LAYERS of which were about
half an inch thick,and toall appearance so clos,.
~ welded that water could not filter through
them
The first LARGO snecpium TINS made in a sin.
ole niece vas e ropnJ nlate Of melI three feet
in diameter. nine inches flick. and unwards of
ton in WEIGHT, On bocomina solid, + was re-.
moved. TO be annealed r. a brick oven, the
month of which is level with Tho yrnrnb nj the
distance of a few feet rho oven was nearly
rad.bo, whom tho snocnlnn, wos sLn, n, xi,hin
il, and from this temperature it was allowed to
become rradualjv cool whom the annealinp WAS
COMPLETED The time reuuired for anneajinp a
plate of this large size i. believe, about three
weeks and vet with ali tbis attention. SO brit
tie is the metal from sudden variations of tenn.
perature. that a warm hand laid upon il in cold
niuht will make il flv in nieces
Following the mass m tho neyt stare in ia
progress. we find If placed. with the face M.
wards. upon a turning apparatus. Here it il
seen moving round SLOWLY immersed partially
in water. in order to be kept cool. while grind
ing or rubbing tool works on its surface. By
means of this grinder. with emery and water,
and the adjusted rotative motions. the proper
parabolic curve. along with A certain degree Of
! smootbness. il nrodnced. after which the sur.
face is similarly polished with resin, and some
other substanccs The reouired curve is ascer.
tanned in the following manner. The grinding
is performed on the ground floor of house. adj.
Joining with a tower several stories high. On
the ton of this tower is erected mast. the sum.
nit of which is ninety feet ,om the specuum
on the grinding machine. To the top of the
mast the dial Mate of a watch is fixed forming
a small round object relieved AGAINST the sky.e
When the workInen wish 70 try the capacity of
the speculum. il is cleared of its grinder. trap
doors overhead are opened the figures on the
4 al NJ, n oro ro,octod On tho snoculnm and This
refcct;on Is soon at the regnlated focal distance
Inv means of a small eve niece in other words.
a Temporary telescope Is formed without a tube
and nv this ircenions vet simple device the spe-
culum in wrnnrbt IN that nice narabolic figure
which brings the incident RAYS to an exact focus.
IOf1he extreme accuracy required, we may OBJ.
tain soma notion from statement of I ord Rose
,b,t an error of a small fraction of hairs
breadth womb DESTROY ali hone Of correct ac-
tion and nr Rnh;n.o, man,i IN. fiat the small
est ineoualitv of local nressur, during the po-
I;sb;n,, rrocoss wouId ba attended with tie re-.
srI, oT ct,nning , vol defined .,,r into a blot
mr. c,,na, y Iho snocnlrm neyer,Loless. was no.
ishpd in the short Spacp OF SIX hours.
: The s,ecnlum. so fortunately COMPLETED, was
: fixed ortedded on three iron plates. which gave
e it supnort. and then transferred to the splendid
# situation in the tube. This. as have already
g noticed is three feet in diameter and twenty
II six feet long, and attached to an apparatus OH
n the lawn, by which it can be brought to bear on
l. any point of the sky short way above the hori-
= zon. The machinery for moving it round and
: raising and depressing it is simple and in
:, gcnous and notwithstanding its size, 1t may
e be adjusted with the greatest ease. Two step
e ladders form part of the apparatus, and by
l. these we mount TO gallery which can be raised
e or lowered to any required height. In order to
o procure an observation, the tube is first brought
!. erv b.ino raised we ascend to il nv one of The
$ i,j,ars IA roaoh;,,r ,ho oalIor,, ,hiob IL =.
:, ''u','e' va ,ea."'"s 're s",'e'!; WY" 10
small rallied platform suinclent 10 hold several
l. persons, find ourselves close to the telescope
n near its MINOR eytremitv and here on lookino
l. ,h.a,,L ~ Ill 49,. -. Ell ., H. 81. .
. '''"sh S"''' c!c-P'eoI i'Neu " '''e '"oe. VIC
al once recognize III tle ooiquely -piaceu MIRROR
IL within. the object OF our observation. The tube
i is of wood hoopcd with IRON and the focal dis
IS t,nre of tho u,urn IL ,vaptvseven foot 7
l., ."e - N; "'1. =, ~ ,h., H., ',.t =,
i the tube remained permanently open. the natu-
e v,nors woulJ optor tberebv and ;niure tho sna
II y, .L - ~ - =; -
. S""" at ','e ioWer eHueht!' , was '.o'"ieo'
telpScOpe