Richmond times-dispatch. [volume] (Richmond, Va.) 1914-current, 1915-04-04
~ ROFESSOR \. a. NICHOLSON, OF
the University of Chicago, has
- ruled 100 00O nerfertIv straipbt

the University of Chicago, has
ruled 10000 perfectly straight
and parallel lines ON piece of metal
inches by inches in area.
This piece of metal is called a diff
fraction grating, and its purpose is TO
split rag 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 color5 Of which 4 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 ray OF white
sunlight are commonly stated TO range
from red at one end through orange
yellow, green, blue and indigo 10 violet
at the other end Before the red end of
the spectrum are the invisible nfra-red
rays, and beyond the violet end are the
invisible ultraviolet rays. The visible
spectrum is divided into an infinite mum.
her of shades of color, and the value OF
Professor Michelson's instrument is that
it measures the largest number Of these
shades so far observed. The colors in
dictate the nature and proportions Of the
metals and incandesccnt materials of
which the sun is composed and reveal
other facts about the condition OF the
luminary. The spcctroscope is our prn-
cipa! means OF studying the nature and
composition OF the sun, the source Of all
life and light The new observations
which Professor Nicholson makes with
his spectroscope are, therefore, in the
lruest sense, messages from the sun
The work OF ruling 100. 900 lines on
plate 6 inches by } inches is probabl,
the most laborious and delicate task
ever carried out. These lines arc exactly
one eleven-housandth equdistant from
one another and they are perfectly par
alel. SO accurate is the parallelinG of
these lines that IL any two of them were
extended for mile there would not be
n millionth part of an inch variation
from the parallel
One of the remarkable uses Of this
spectr6scope is that it will measure the
difference between the wave lengths Of
various colored rays down TO a millionth
part OF ccntimetre, or one three mil
liOnth OF an inch, recording colors that no
human eye ever saw. BY means of pho
tographic 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-callcd primary colors-red.
orange, yellow. green, indigo, blue and
violet. The difiraction grating will split
the ray into 10000 different shades of
color.
How to draw the lines on the grating
was a great problem. apart from the tre-
mendous labor involved. Several failures
we're made before q satisfactory method
OF doing the work was reached. The
lines are drawn by diamond point. and
il had to be done so delicatey that there
was not the deviation Of the breadth Of
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