St. Mary's beacon. [volume] (Leonard Town, Md.) 1845-1863, 1862-03-13
PAPERS FOR THE PEOPLE.
The Telescope ard its Marvellous Rev
elati0ES-

IL - reiateu OF the Wise anu ltIuStTtOuS
Galileo that report having reached hin,
Of til. construction "f an optical instru-
ment by m-ans Of whicl. distant oljrcts
appeared a. if they were near. that phi
l"snphcr, forcibly struck with the advan-
tagc which might be derive from the
cunt,ivancc, instantly directed his at
tcntion to the discovery Of its nature
The night after he heard the account, the
construction Of such ali instrument occur
red to- him; the day following. he put the
sev, raj parts Of it together; aud the trlcs-
cope which he thus invented is still! cal
I'D by bis naa,e. With that noble frank
nrss tor which he was remarkable. aud
which ought always to distinguish the
true philosopher from tn. cmpiric. he
forlLwi,h explained publicly the structure
and wonderful uses that might be made Of
the instrument: and shortly aftcrward, in
deserved acknow lr,lgmcnt of his emincn.
scicntitic merit, The Republic Of Venice
more than iriplrd the salary attaching 90
his protessorship
EXTRACTING AND RErLECrISG TELESCOPES
Astronomical rcfracting Telescopes
may be described as consisting essentially
of two glassrs: The ohc named the object
glass receives the rays preceding from
the object and forms an image of it in
It's focus; while the "th,r-the glass
serves for lacking at this image The
enlargement, produced by this kind of tel
csccpe proceeds from two causrs The
image form, d iii the fncus is already en-
largcd when seen by the naked eye. be-
cause it is at u distance Of but seven or
eight inches from il; distance much less
than that which separates the lens from
the focus. SO that it is thus seen ui,.ler an
enlarged angle; but it's enlargement is par
ticularly due TO the cye-gla<s. which is y
lens Of very short focal distance. These
astronomical rcfracting telescopes are very
powerful, semc of them magnif.ing ~
much as a h.illion times or m"rt, thus rcn-
dering them of great value.
Ecfccting telescopes consist of pol
i>hcd metallic reflector, in the focus OF
which the Image is formed by reflection
l.ut as this Image csl.not be seen through
the reflector, small mirror is employed
to project i, latrrally, or else behind the
r. fec,or, through small opening made in
j, for the purpose. The original rays are
supposed to strike parallel upon the refrc-
tor. This double reflection il attended
with the Inconvenience If considerably
diminishing the light; f"r it is we'll known
that the most polished mirror hardly re-
fleets more than half the light incident
upon it. Thus. with equal dimensions. a
rrfrcting telescope has only fourth part
of the power Of refracting telescope. for
rcfraction does not sensibly diu,inish the
light. 10 measure tue height Of the stars,
aud for multitude of other operations,
refracting telescopes have in their field Of
view metallic threads. variously arranged,
AID of extreme dclicacy. being consid-ra-
bly, finer than spiders threads. The
,neans by which they are procured is in
genious. The threads. which are If pls-
tina. are FIRST drawn out. as fine as they
can he made with the wirc-drawing APP
paratu>: they are then put into cylinders.
into which melted silver is poured: and
thus they form the axis IT silver cylinders.
which arr themselves subjected to the
wire-drawing process.
PEoDrcrI OF oBJEcr-GLAssEs.
The great difficulty experienced in Sc
curing telescopes Of the desired p"wrr. is
in regard to the optical glass; aud. until n
quite recent perioi. the glass-maker has
been unable I" supply. with any certainty.
even moderately large mass's Of faultlcss
glass. To he thus faultlcss., for optical
purposes. glass muss have uniform dem
sity. high rrfrac'ing Power-if flint glass
-colorlessncss. freedos, from s,riH. snd
lastly. an absence Of air-bdbtles I"
meet these requirements has staggered the
resources Of fhc whole scientific world
The difficulty has been neasurally over
come. however; aud glass dises Of any re-
required dinen.ians may now he mace.
II . ,,,,.;l. ,.l,le 4. gra. ..f .ert ,iatr I'll ak