Evening star., 1898-07-23

| temperature affected it. During the first
winter after polishing was begun only
| nineteen hours were devoted TO actual work
| upon the glass, and the succeeding winter
| even less time than that. The total num-
| Ger or hours work on the glass from tina
| start to the finish was something under
700. And yet to complete ii required nearly
the full two years which Da. Peate pledg-
| ed the bishop at the conference. The lens
which is sixty-two inches in diameter. five
ana three-eiehths inches thick and weighs
| l,5oo pounds, is perfectly hawless piece
| OF glass and when fully polished looked
more like pool of limpid spring water
| than a great telescope lens. destined Ia
| bodies.
| No better idea of the nicety with which
| the glass had to- be handled can be mad
| than by a description of some OF the tests
final polishing.
| BY means of an Ingenious mechanical
| device, the table on which the lens Law
was turned up so that the glass rested
perpendicularly on one edge facing lnta
me testing room. a low-ceiled, narrow
gallery about 100 feet long. that projects
| from the rear OF the primitive work sh0D
Prepafatory to making any of the tests
Or; Peate opened the big door at the far
end of the gallery. A flood of light nourad
| in and suffused itself over the nolished
| surface OF the great mirror which reflected
back with startling clearness and briIlisncy
| every blade OF grass and passing cloud
Testing the Big Lens.
All the tests to which the lensmal1er sub.
Jected the glass were very simple ones, but
embodied the most exacting optical prfuci-
pies, whereby the perfection of speculum
may be determined with infnitesimal &C.
cLracy: For the first one, DIR. Peate went
up TO the lens. and placing his thumb upon
AZ, requested the correspondent to note
Mheh ne had held ii there fifteen seconds
The time up, he came back about o. feet
| 10 small table on which was a common
on lamp. cylindrical tin tube and a small
soInuaIq ,In "a supporting vertically brass fer
ruie' ne Hghted the lamp. placed the tin
tnpe over turning il so that only The light
from hole in the side. smaller than a min
point shone on the glass. He then sat
doV n back of the table and shifted tba
lamp and ferrule about until their adjust
ment seemed satisfactory. He arose and
mouoned me to take the seat, directing me
70 close one eye and look past the edge OF
the ferrule with the other After a mo-
me mt OF searching for the optical point NV
eye suddenly caught a gleam and the whoIa
surface of the big lens appeared effulgent
with a mellow light, like the surface of the
Iull moon Near one edge was small dark
spot. DO you see that spot?'' uueried ths
DOCTOR That is bump caused by the ex-
p1hslon or the glass under the heat Of my
tnumb- 1t is less than one ffty-thousandth
OF an inch high. and yet YOU see IL with the
little point of light that escapes through a
mole too small to accommodate a pin, II
Is impossible to measure IL or detect ft in
any oiher way than by this simple light
test You are seated at the redius of curya-
ture ana the straightedge is merely an as
sistahce TO your eye in finding and keeping
the point at which the light reflected from
the glass collects. 1t is by this test that /
low in places
he then pointed out a spot Just q shade
uaFker thSn the rest of the surface whera
IN polishing that afternoon he had left tba
glass raised about one one Lundred-thou-
sandth of an inch.
The next test was one of striking baoutv
ana Illustrated the wonderful sensitiveness
or the glass. DIR. Peate walked forward
and merely held his hand near il. looking
aiCf the ferrule. the surface Of the glass
was seen to be all disturbed and covered
with great billowF clouds of light Ptow-
ing his breath across it caused it to fairly
Doll with vaporous clouds and waves
Ihat Is the action of heat" he explained.
Ihe presence of even a moderately warm
BODY near II affects it thus and so does a
inference IN temperature bet tween the asr
without and within the shop. Consequently
must keep my glass at a uniform tenn
perature with the atmosphere or its s,,r
race becomes so disturbed that / cannot
give II an accurate test. That is also ona
reason why 1t takes so long time as two
years TO complete it and explains why
could not work on it more than a few bours
last winter"
Searching the Sky.
After every known optical test has been
given a telescope lens while il is heinz
made there is one final and best one thax
can only be made when it is conpIetrs
That is to search the sky with IT. DR.
Peate has twice put his glass 10 that final
feet. P0
1t was while the great lens was resting
IN us carrying case that he conceived the
idea OF turning 1t on the heavens Accord
lllgiy ne silvered lis face. Then he wheeled
the case out onto a small platforn, I'm fbs
rear of the workshop. Thirty-two feet ont
IRON the platform he constructed ro,Ieb
scaHolding. Thirty-two feet is the ais
tarce from the face of the big mirror 1t
which its rays of reflected light are To-
cuSed He had next constructed a 32-foat
wooden arm made like huge crutch. The
open ends Of this he placed on ej, nor SD
OF the glass and the other closed end ,,,aS
raised 10 the top Of the scaffolding ON
II ne placed the eyepiece through which
the focused hight Is admitted to the eve
linen tlting the glass back as far as ba
could one starry night a few weeks AGO
the venerable astronomer climbed ND his
rickety scaffold and during four hours sat
uiieohiortaDly on the topmost round of the
ladder studying the heavens and searchfnr-
ly noting the working of his precious mir
ror.
1T was the greatest optical pleasure
nave had since began the study of astron-
omy and the making of lenses" he said.
There i sat pcrched on the ton round az
my ladder for four long hours 1 did not
Ieel the cold. nor the hard ladder under me-
spectacle of the heavens which nv big
glass revealed to my eyes. 1t was irnpos-
slble for me to turn the glass on any IA
miliar star or on the young moon l could
only get it on a vacant spot IN the heavens
near the constellation Of Corbus below the
Dragons tall of Hydra. But in that space
empty to the human eye and even to a
fairly powerful glass, 1 saw numerous
beautiful stars. 1t was a splendid pano-
rama. for not being able to move my glass.
L had perforce to be content with watching.
the heavens slowly pass across the surface
OF the mirror, star after star"
As an Equatorial.
The Peate Lens. for such it will undoubt-
edly be called, will be mounted as an equa-
torial in tube something over thirty-two
feet in length.
The cost of so mounting it will run I'D
into the thousands of dollars. TelescoDes
to be mounted as this one are called New
tonian telescopes, because of the principle
OF interior arrangement.
The mirror is perpendicular to the axis
and the reflected rays falling on a small
lnclined-plane mirror at the focusing point
are turned out to one side of the tube into
the eye piece The essential difference be-
fha TO 4 81