The Providence news. (Providence [R.I.]) 1891-1906, 1897-03-04


sure of the Photographic plate be contin-
ued long enough. The construction OF the
new telescope is based upon the deductions
arrived at from this knowledge.
Telescopes are of two kinds the reflect
| ing" which employ large concaye re-
| nector from which is reflected the observed
object TO a small lens in the eycpiece, and
"refracting" telescopes, which use largo
| glass lens called the "object glass" The
first kind give more light than the latter.
The latter give better definition.
| The new telescope will consist Of a huge
refractor of metal, carefully ground to a
proper curve, and highly polished, and
from its great size will be constructed and
mounted in sections. When the parts arc
assembled in place to form the complete
mirror il viii measure 200 feet in diameter.
TO mount SO gigantic an affair would re-
quire frame work of enormous dimensions
| and besides, any Improvement of the
whole would be extremely difficult; GER
tainly no delicacy of movement could be
attained. The huge concave mirror is
|
of steel and brass, so arranged as to com
pensate for expansion aud contraction,
and thus preserve tho symmetry of the
mirror under changes of temperature.
| This framework rests upon n tank, or float
| which is supported In pond or basin of
water. BY this means stability of equi-
poise is secured the vibration of the
| IL oil IN, mir m nd hx- IN
| well-planned system of movable weights
the mirror may be made TO incline at
desired angle or turn from one point of
| the heavens to another.
The image reflected from this giant
speculum mirror is received at the proper
focus by the lenses of the eycpiece, which is
situated 1000 feet distant from the surface
of the mirror. This lengthy focal distance
is necessary for the purpose of keeping
the reflected rays as nearly parallel as pos
| sible so that distortion at the focal point
| may be diminished to minimum and a
finer definition obtained than would be
possible should the rays converge at the
acute angles
Notwithstanding that our moon is
called dead" star and is supposed to
have no heat of its own, yet it reflects to
us the heat as well as the light Of the sun,
and every stellar body sends some heat TO
the earth. The concentrated rays Of the
| huge mirror used i'm the new telescope
| would convey sufficient heat from the
| moons surface To destroy the cyesight of
| any observer who had the teinerity to look
| Il. nIx
this translucent prism of rock salt is
| placed in front of the eycpicce, between it
| and the big mirror, which absorbs the heat
rays 1t, however very materially dims
| the image of the object under observation
and when the telescope is used for photo
graphic purposes the salt prism is re-
moved.
To satisfactorily observe celestial
object, as star, the telescope must be
made to "follow the star" that is, it
must be made to move in "a contrary
direction TO that of the earth In ordi-
| nary astronomical telescopes this is ac-
complishcd by II clock, whose works con-
meet with tho telescope and koepl it
constantly pointed at the object observed.
| But the giant reflector is too large for
this, and its gaze is therefore confined to
objects in the zenith or close TO it. For
tunately, the rotation of the earth upon
her axis brings most of the desirable
heavenly objects to the zenith at one
time or the other. The huge telescope
here described is movable only To a very
slight degree, and used as an observation
instrument for the human eye would
prove unsatisfactory. But the photo
graphic eye is the one intended for its
gaze. Photographic science has narrowed
down the length of time of exposure
necessary to produce perfect negative to
the one ten thousandth part of second
while the perfection attained in the pro-
duction of Photographic films makes IL a
comparatively simple task to obtain n
picture so infinitcsimally small as to re-
quire the highest power microscope to
make visible to the human eye the pho
tographed view, which is however, com
plete and clear in every.dctail.
Used as intended, the giant reflector
will have no cycpiecc, but i'm its place
will be specially constructed photo
graphic camera, fitted with system OF
clockworS which rotates a long ribbon OF
extremely sensitive film, and while in
operation opens and closes n shutter In
front of the film with rapid motion.
The surface of the film is adjusted at the
exact focal point Of the huge mirror with
such dclcacy as to produce upon the film
an image no larger than the head Of q
pin The pictures thus taken may be,
after they are fixed" enlarged by any