Omaha daily bee. (Omaha [Neb.]) 187?-1922, 1915-04-04
~ RoFESSoR A. A. NICHOLSON, OF
- the University Of Chicago, has
= ruled 10000 perfectly straight

the University OF Chicago, has
- ruled 10000 perfectly straight
and parallel lines on a piece OF metal
6 inches by 8 inches in area.
, This piece of metal is called a diff
fraction grating, and its purpose is to
split ray of sunlight into the greatest
number of shades of color ever seen. 1t
is the basic part of the largest and most
perfect spectroscope ever constructed.
The spectroscope, as most of us know,
is an instrument that enables one to see
the different colors of which a ray Of
sunlight is composed. In the simplest
form of spectroscope the ray is split up
by passing through a glass prism. In
Professor Michelson's instrument it is
split up bv the lines on the diffraction
grating.
The colors composing a ray of white
sunlight are commonly stated to range
from red at one end through orange,
yellow, green, blue and indigo to violet
at the other end. Before the red end Of
the spectrum are the invisible infra-red
rays, and beyond the violet end are the
invisible ultraviolet rays. The visible
spectrum is divided into an infinite num-
Der of shades of color and the value of
Professor Michelson's instrument is that
1t measures the largest number of these
shades so far observed. The colors in
dictate the nature and proportions OF the
metals and incandescent materials OF
which the sun is composed, and reveal
other facts about the condition of the
luminary. The spectroscope is our prin-
cipal means of studying the nature and
composition of the sun, the source OF all
life and light. The new observations
vuvftI
his spectroscope are, therefore, in the
truest sense, messages from the sun.
The work of ruling 120, 900 lines on
plate inches by 3 inches is probably
the most laborious and delicate task
ever carried out These lines are exactly
one eleven -thousandth equidistant from
one another and they are perfectly par
allel So accurate is the paralleling of
these lines that if any two Of them were
extended for a mile there would not be
"a milllonth part of an inch variation
from the parallel
One Of the remarkable uses of this
Bpectroscope is that it will measure the
difference between the wave lengths of
various colored rays down to a millionth
part of a centimetre, or one three mil
lionth of an inch, recording cOlors that no
human eye ever saw. By means of pho
Geographic plates many facts will be
learned from the spectroscope that the
eye cannot detect
The old original prismatic spectre
scope separated a ray of light crudely
into seven so-called primary colors-red,
orange, yellow, green, indigo. blue and
violet The diffractiOn grating will split
the ray into 10000 different shades of
COlcr
How to draw the lines on the grating
was a great problem, apart from the tre-
mendous labor involved. Several failures
were made before a satisfactory method
of doing the work was reached. The
lines are drawn by a diamond point and
it had TO be done so delicately that there
was not the deviation of the breadth OF
a diamond point between any two OF the
10000 lines.
How to space them accurately was
one Of the greatest difficulties to be over
come. Professor Nicholson tried to do
this at first by placing his grating in a
mercury bath. He would draw one line
and then place the grating edgewise in
the mercury bath. Then a measured