26 
menfe body to any part of the heavens 
will be clearly feen. 
the chief parts in their order; and firft, 
of the tube itfelf. \ 
The tube .1s- made of rolled or fheet 
iron, joined together without rivets, by 
afimilar feaming to that which js ufed 
for iron funnels for ftoves; the thicknefs 
of the fheets is fomewhat lefs 
36th part of an inch, or it may be found 
more accurately by taking a fquare foot 
of it at the weight of fourteen pounds. 
Great care was taken in fo joining the 
plates of which the tube is compofed to- 
gether,- that the cylindrical form fbould 
be fecured, and then the whole was 
coated over three or four times with 
paimt, infide and outfide, to fecure it 
againft the damp. The tube was formed 
at a fhort diftance from its prefent place, 
and removed with great eafe by twenty- 
four men, divided into fix fets; fo that 
two men on each fide, with a pole of tive 
feet long in their hands, to which was 
affixed a piece of coarfe cloth, feven feet 
long, going under the tube, and joined 
to a pole of five feet long, in the hands 
of two other men, aflifted in carrying 
thetube. The length of the tube is 39 
feet 4 inches, the diameter 4 feet 10 
inches; and, upon a moderate computa- 
tion, it is fuppofed that a wooden tube 
for the fame purpofe would have exceeded 
this in weight by at leat 30co pounds. 
The length of the iron plate forming the 
tube, and compofed of f{maller ones 3 
feet 10 inches long, and 234 inches broad, 
is nearly 40 feet, and the breadth 15 
- feet 4 inches. 
The great mirrour which, by proper 
methods, was brought to the lower part 
of the tube, is made of metal, 493 inches 
in diameter; but the concave part, or 
polithed furface, is only 48 inches in di- 
ameter. Its thicknefs is 34 inches ;, and, 
when it came from. the caft, its weight 
was 2118 pounds, of which a fmall quan- 
tity muft have been loft in polifhing. An 
iron ring, 49§ inches in diameter, within 
4 inches broad, and .1$inch thick, with 
three ftrong handles to it, goes. round the 
Mirrour, and a flat cover of tin 1s made 
to correfpond to this ring, that the mir- 
rour may be preferved trom damp; and, 
by an eafy contrivance, tis taken off and 
fixed on at pleafure. 
At the upper end, the tube js open, 
and direéted to the part of the heavens 
intended for obfervation, to which the 
obferver’s back is turned, and he, ‘ftand- 
ing on the foot-board vilible in the plate, 
looks down the tube, and‘ perceives the 
Herfehel’s Telefcope. 
We fthall treat of 
than a - 
[ Feb. 
objet by rays refleed from the oreat 
mirrour, through the eye-gials at the 
opening of the tube. Near the place of 
the eye-glafs is the end of atin Pipe, 
into which a mouth-piece may be placed ; 
fo that, during an cbfervation, a perfcn 
May direct his voice into this pipe, whilft 
bis eye is at the glafs. This pipe is 14 
inch in’ diameter, runs down to the bot- 
tom of the tube, where it! goes into 2 
turning joint, thence into a drawing tube, 
and out of this into another turning 
joint, from whence it proceeds by a fet of 
fliding tubes towards the front of the 
foundation timber. - The ufe of this tube 
Is to convey the voice of the obferver to 
his affiftants:; for, at the lat piace, it 
divides itfelf into two branches, one go- 
ing into the obfervatory, the other into 
the werkman’s room, afcending in both 
paces through the floor, and being ter- 
minated in the ufaal fhape of fpeaking- 
rumpets. Though the voice paffes in 
this manner through a tube with many 
infleétions, and not lefs than rr feer, 
it requires very little exertion to be well 
underftood. zs, 
‘Fo direét fo-immenfe a body to any 
part of the heavens at pleafure, much 
Ingenuity, and many mechanical contri- 
vances are evidently necéflary. The 
whole apparatus refts upomrollers, and 
care was previoufly taken’ of the founda- 
tion in the. ground. This confifts of 
concentrical circular brick walls, the 
cutermoft 42 feet, the ianermoft 21 fect 
in diameter; 2 feet 6 mches deep under 


ground, two feet 3 inches bread at the 
bottom, and 1 foot 2 inches ar the top, 
capped with paving-ftones, about 3 inches 
thick, and 12} inches broad. In the 
centre is a large poft of oak, framed ‘'to- 
gether with braces under ground, and 
walled faft with brick-werk, to make it 
fteady.. Round this centre, the whole 
frame.is moved horizontally, by means of 
20 rollers, 12 upon the outer, and 8 upon 
the mner wall. 
The vertical motion is given to the 
-telefeope by means of ropes and -pullies, 
as feen in the plate, pafling over the 
main-beam, fupported by the ladders. 
Thete ladders are in length forty-nine 
feet two inches; and there is a moveable 
gallery with twenty-four rollers to eafe 
its motion. The {mall fiair-cafe vifible 
in the plate is intended for perfons who 
wifh to afcend inro the gallery, without 
being obliged to go-up the ladder. The 
eale with which the horizontal and ver- 
tical motiéns may be communicated te 
the tube will be belt conceived from a 
remark 
