The Anaconda standard. [volume] (Anaconda, Mont.) 1889-1970, 1896-05-24

glass-and they are much more numer-
Gus than the good ones-has noticed
that objects often appear bordered
with the rainbow colors. This is be-
cause the lenses OF the glasses are not
perfectly corrected for color" as the
technical phrase is. Every lens. IL
something were not done to prevent
would act in this way. for every lens
acts as a prism: II not only brings the
light rays to a focus. but splits them
into their prismatic colors. The bigger
the lens the greater the separation of
colors, so that when large telescopes
were first attempted this was thought
TO be an insuperable obstacle to any
increase in size. Then the present
method of correction" was discovered.
BY skillful combination of two kinds
OF glass, ii was found possible to re-
combine the colored elements of the
light without entirely doing away with
the bending to focus that gives the
lens IL power. These compound lenses
were called "achromatic." that is, col
orless; a name that was not quite accu-
rate, for IL was impossible to do away
entirely with all the Objectionable col
ors II the lenses were so combined as
to make the red disappear. there was
still some blue and vice versa.
With the small telescopes formerly in
use the little fringe of color that was
left over was of no great account. and
this method, with its subsequent modi-
fications and improvements. was long
regarded as a final solution of the prob
lem. But the color question" in as
tronomy as In sociology. will not down.
and only grows more perplexing with
the progress I'm the other branches of
the science. With the huge glasses
now in use this little residue of blurred
color, due to what is known to astrono-
ls.r
tion," becomes a serious obstacle to ac-
curate observation. 1t is this which
Professor Hastings has succeeded in
removing.
The Yale professor was at work last
summer on a problem in mathematical
optics. when very slight thing-the
sign of an algebraic term-attracted
his attention and made him pause.
The sign was precisely opposite to that
involved in the equation for color-cor-
rection. 1t occurred to Professor Hast
ings that by giving a lens the proper
shape these two algebraic terms might
be made to balance and destroy each
other, or, what is the same thing, that
the proper shaping of the lenses might
destroy the color fringe Further calcu-
latfons confirmed his views. and long
and laborious mathematical investiga-
ton indicated the exact shape to be
given to the glass. Experiment showed
that he was correct. He had solved a
long-standing problem i'm telescope op-
tics with pencil and paper!
The value of the new method was
first demonstrated by constructing
small telescope for use with a spectro-
safe. This has proved a complete sue
cess, the color fringe being entirely de-
stroyed; and there now seems to be no
reason why the method should not be
extended to the very largest glasses.
The next experiment in this direction,
Professor Hastings says, will be a four
and half-inch instrument to be made
by Brashear. Doubtless" says the
professor, in a recent letter. lit viii be
quite a long time before we shall be I'm
a position to advise very large teles-
copes, although l can see no obstacle
to their success; but the great cost of
such instruments demands the utmost
caution i'm procedure"
In country that has produced the
Lick and the Yerkes telescopes, and
that has the reputation Of unbounded
generosity in scientific matters, Il is
not likely that the question of cost will
be allowed TO interfere for a very long
time with the complete development of
such a valuable invention-the product
of a typical American brain.
Arthur T.. Bostwick. PHI. ID.