The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1925-11-04

Wilson Observatory.
to q focus before the red (chromatio
~aberration). II was almost $50 years
before an English optician discovered
that these defects could be overcome
by making the objective of two
pieces of glass, the outer piece con-
vex and made Of crown glass, and
the inner concave and made of flint
glass. Meanwhile, the rejecting
telescope, invented in 1859 by Sir
Isaac Newton, had come into use.
Passes to Mirror
In the Newtonian r~eflecting tele-
scope the light passes the entire
length of the tube to a curved mir
ror, called the 'speculum," which
reflects the rays back in the shape
Of a cone to a prism or diagonal re-
Hector. The prism diverts the rays
at right angles to an eyepiece at
the right side Of the tube. Such q
telescope is free from chromatic
alteration, but the position Of the
eyepiece makes it more awkward to
use. In another form Of the re-
fleeing telescope, the Cassegrainian,
the con of rays reflected from the
speculum is intercepted by another
curved mirror placed near the other
end reflected back through a hole in
the center Of the speculum Of the
eyepiece.
Both r~eflecting and %refracting tele-
scopes are used in modern as
Economical observatories. The adj
v~antages of the reflector are it's
~cheapness and it's perfect "achro-
matism" Freedom from outside
c%olors), while the main advantage of
a refractor is it's permanence and
freedom fro mtrouble after once be-
ing well adjusted. The largest tele-
scopes in the world are r~eflectors;
the king Of them all is the 100-inch
reflector at Mt. Wilson, Cal. A
practical drawback to the reflector
is that the ~speculum furnishes and
needs occasional repolishing If of
metal and r~esilvering if of glass.
The Mammoth Yerkes forty-inch
~refIactor can be used advantageous.
ly to give 1000 diameters, and higher
powers r possible.
Man Most Important
The most important part Of a.
telescope, a great astronomer says.
us the man at the small end" Next
in Importance is the objective lens
or the speculum; this must be made
with almost miraculous precision.
The surface must be accurate to the
fifty-thousandth part Of an inch, and
months, even years, Of labor are
often required to cast and polish a
single objective. So sensitive to
changes Of temperature Is the great
9,000-pound 100-inch mirror at
Mount Wilson, Cal, that 1t is kept
in a water jacket during the day
time. The mounting and control
ling mechanisms of telescopes are
also marvels Of human ingenuity.
Many modern telescopes are so con
jects and spaces in the field may be
made in thousandths Of an inch, by
means of the micrometer.
In all astronomical telescopes, the
image seen at the eyepiece is in
verified. In the smaller telescopes or
Eyeglasses to be used on land, IN ad.
ditional lens or system of lenses has
to be introduced to re-invert the i'm
age, o that it is seen in the same
position as the object. The opera
or field glass Is a pair Of small tele-
scopes with concave lenses for the
eyepieces. The most efficient and
modern instrument Of this type,
called the prism field glass or "bi-
nocular," has two ~reflesting prisms
in each tube. This gives it as much
magnifying power as could be OBJ
tanned with an ordinary field glass
three times as long, besides permit
ting the use of a better type Of eye
piece, which gives a much larger
field Of view with better definition,