The sun. [volume] (New York [N.Y.]) 1833-1916, 1897-12-05
THE MODERN TELESCOPE.
zRIUMPHs SECURED BIZ OPTICAL
AND MECHANICAL SKILL.

aecirty or Mechanical Engiusers-Vvide Use-
rainess OF tho Telescope - Diniculties OF
Making tho Flint Ginss for nsiE LeBncs.
Worcester II. Warner. President Of the
American Society OF Mechanical Engineers, de-
livored an interesting address before the society
at tho beginning Of the annual meeting at tho
clubhouse, IL West Thirty.iirst street, last
Wednesday. upon the history and practical use
Of tho telescope.
"The earliest telescopos," Mr.. Warner said,
CONSISTED of two lenses held In their relative
positions by insertion In q tube. Tho object
glass. or objective, was of double convex form.
and the eye piece was n double concave lens.
the distance of these lenses from one another
being tho difference Of their principal foci, Just
as In the tubes of our cheapest opera glasses OF
to-day. The modern opera glass, however,. mag.
miles but about gig diamcters. while Calico
succeeded in making, on this principle. u tele-
scope which magninod 80 diameters. With this
he discovered tho mountains on the moon. tho
phases OF Venus. and the four satellites Of
Jupiter. Two serious optical difficulties, called
schromatic' and spherical alteration, cause
Tho earlier astronomers great trouble; for, even
In Galilco's telescopes, small as they were, q
fringe of rainbow tints surrounded cvsry object
viewed, and the objects, too. had n moro or less
.hazy or indistinct appearance. caused by tho
spherical alteration OF tho single lens used by
him. while tho higher tho magnifying power tho
more manifest were these defects. But at last,
In 1893. the English optician. Dolland discov.
cred that the dispersion Of light was variable
whom refractcd through different kinds OF glass.
With this fact as q key, nc constructed object
glasses having two lonscs OF such form and re.
fracting power that one would correct the error
OF tho other. and thus eliminate entirely the
spherical alteration as well as the greater part
Of tho chroinatica bcrrr ton.
Each advance in the optical efficiency of the
telescope necessltatcd equal improvement in
mechanical means for adjusting and using the
instrument. At first II was sim ly held in tho
hand, and even as crude methods of support
came gradually into vogue they were OF small
use otherwise than as approximately holding
the tube in position. Then came n better mode
OF mounting by which the telescope was made
to follow the motion Of tho stars. it being moved
at first by hand and then by clockwork.
with the combination of mechanical and
optical efficiency the modern achievements in
telescope building became possible. A modern
French engineer has devised a form OF mounting
viii h is called the equatorial coude, or elbowed
telescope. Remember, If you please. that tho
temperature of nm observatory must be kept as
nearly as possible that or the atmosphere out
side. otherwise currents of air would make tho
definition imperfect, and even obscure the lesser
stars; and remember. too. that since definition
Is often best in cold weather. the astronomer
must be Injured to work in appalling tcmpera-
lures. Moreover. unless there bc an oleva!ing
floor to his observatory. he has the added dis
comfort Of putting himself into all sorts of atti.
tudes while observing. 1t is TO obviatc these
that the coudG was designed. Hero
the polar axis forms part of the tube, the OBJ
server looking through the upper end. while
hitting comfortably in his warm room. in an at.
titudc as easy as IL using a microscope"
Then Mr. NNnrnrr lnSnrthnI thn ,,1rrtt--- 80
the great Yerkcs telescope.
The weight OF the 40 inch objective, with
us cell, is 200 pounds he said. The weight
alone weighs 6 tons and is 81 foct long. Now,
the column supporting these heavy movable
convenient form. TO secure these results it is
made rectangular in shape, and is cast in four
sectioa has n 6road, extended bnse, ii by Is
Iest, anchored IN the %s1iilest manner to the
tains Tho driving clock and its attendant
mechanism, while surrounding this section is
the equatorial head, supporting all of the nova.
The great tub, must be as free from ficxure
as possible. and of such form ana construction
as TO insure minimum weight. 1t Is made OF
Is made to carry not only the micrometer and
graph ana other, physical and astro.physical
apparatus. Az the eye end, too. the observer
motions in ,declination and right ascension, as
well as the buttons operating the electric clamps
uhA .niDtlOuS. Inc weight o. the tube. tho |
axes. and their connections, all OF which must
move when this telescope is following the appar-
ent motion of n star, is twenty-five tons.
" Provision must be made for conveniently |
pointing This monster optic tube to any part Of
the visible heavens. This is roughly and quickly
done by the electric motors, one giving the mo-
tion in declination and the other in right ascen.
sion. Two smaller motors are also provided for
EiSing slow motions in both directions. BY the
aid or these motors the astronomer is able to
bring the star to the centre of the field. in coin
cidcnce with the micromcter wire. These move
mcnts must also be easily made by hand, either
by the assistant on the balcony OF by tho astron- |
THE driving clock, which is located in the
upper section. must DO able to carry all this
great weight in exact sidereal time. so that the
star shall appear to stand still as it is bisectcd
Dy the spider web Of the micrometer in the focus
tanned by a weight Of $50 pounds, Which, When
The clock is IN motion, falls lia feet per min
Sts; mhe whole En dc meenanism q the driving
be instantancOusly communicated to the polar
AXIS ,by electric clamps and also by hand, and
tnut IL snail provide tor conveniently changing
the speed from stellar to lunar and 10 solar rates.
FINALLY, since the success of many important
lar motion OF the driving clock. an electric motor
must DC Introduced for automatically keeping
There is a popular idea that detectives are
made large in order to magnify enormously.
liSht. The pupil Of the eye has a diameter Of
only about one-tifth OF an inch. The telescope
Pc serfes 10 ihGremss the humber OF rays TINT can
many as fall on the surface OF the objective.
Ihe relina is thus. as Prof. Holden SAYS, 'virtu-
ally Increased III the ratio OF the square OF the
diameter CT the objective, 10 the square of one
MIN ofan inch. Thus. with u Pinch aperture. tho
humber OF trays collected Is 100 times as great as
inc number Collected by the naked eye Figur.
ms thus, too. the star seen through the Lick OBJ
oeSilve Is more than 10000 times as bright as
when seen with the unaiGcd eye"
VI the uses Of the telescope Mr.. Warner spoke
thus:
sensational discoveries are reserved for
targe instrunenis, ana one such may yet reveal
TO Us Tho trans-Neptunian planet so long and
NulUly sOuHUl Ill our OWN day. Tho original naa
Of the telescope WAS 10 study the motions Of
heavenly bodies. 10 mere observing nave been
euded photography. photometry. spectroscopy,
ana SO, IN process or tlnio. the telescope has
PASSED through a form OF evolution that allies
IL 10 the history of civilization. While astron.
ony. IS We know, is OF all sciences tho
one most removed from the sphere OF COM
Mercinl results. yet the telescope, in some
Torn, or another, is the one and only means
we nave OF navigating ships. of measuring
wide eNpanscs OF territory. OF determining lati-
hbnue ana longitude, and OF keeping time.
The telescope 10 Just as Indispensable, too, to
re surveyor. In laying out a railroad across
the continent his position is found by observing
his latitude and Longitude. The distance from