The Cook County herald. [volume] (Grand Marais, Minn.) 1893-1909, 1898-04-09
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to Dublin:

. tronomer, says the
New York Tribune.
| -. This news calls
! fresh attention to
unique, almost unknown and re-
markable piece of machinery, the ruiz
Ing engine of a professor of Johns Hon
klns university, wherewith an impor-
tant part of the instrument Just men,
toned was made. The object of a spec
troscope is to analyze light from a star.
neDula, the sun or some other lumi-
nous object. In this operation the i'm
age OF narrow slit is expanded side
ways until it is converted into a long.
prlsmatlc band or spectrum, violet at
one end and red at the other. For
studying most of the heavenly bodies.
glass wedges or prisms are employed
10 perform the work. These, properly
arranged, will render good service
| "here a high dispersion" or magnifi-
cation is not desirable. But with the
sun, whose light is so intense that it
Will stand great. dilution $50 to speak,.
1ar more considerable dispersion is
entirely feasible. And the astronomi-
cal spectroscopist is anxious to produce
this effect, in order more completely to
separate cross lines in the spectrum.
winch are ordinarily too close together
to be properly distinguished. The
whole point of certain researches de-
ponds altogether on the possibility of
Identifying a. suspected line positively
ana OF measuring it's position in the
spectrum with precision. Such separa-
ZION can be much better obtained with
a grating than with a prism. There
are two kinds of gratings. One con-
slsts OF glass, on whose surface a Sc
rles OF fine, parallel lines are ruled. The
other Is a highly polished metal plate.
similarly engraved. The former lets the
hght shine through it; the latter re-
fects it. In either case the effect is
to produce spectrum exactly as a
prism does. To the metal plate a slight
concavity is previously impaired, so
mat 1t will focus the image without
use OF an extra lens. It is the latter
type OF grating which was now intro
duced into the new spectroscope. Bras
near made the mirror, gave it Just
enough curvature to make the focal dis
lance some twenty-odd feet, and then
sent:lt to Baltimore for treatment in a
laboratory there. 1t is stated, no doubt
With truth, that the lines on this mari
tlcular grating are so fine and so close
together that there are 10000 to the
inch! A simple comparison will en-
| able one easily to realize what this
means. In the majority of books there
are from 200 to $50 leaves to the inch
when the covers are pressed firmly to-
| gether. In small minority, the num-
Der will range from 300 to $50. These
| lalter hgures represent rather thin ma
| per- Now, if we could split one of the
very thlnnest of these leaves into 900
layers OF uniform thickness. the pro-
duct would be equivalent to 105, 900 to
| the inch, or little less than the num-
| Der OF lines in this spectroscope graf
ing. 1t must be remembered more
| over, that there must be little space
between the lines if one is to he dis
| t1nct from the other Therefore. if an
inch be divided up into 1000 900 eo,1a1
parts, nine Of them would be covered
by line and space. It is stated in
one OF the news dispatches that the
| space was 3,O00,00Oths wide: from
| which it must be inferred that the line
was 6,OOO,O00ths of an inch wide! OF
course it is impossible to see such lines
with the naked eye Only very DOW
erful microscope would reveal them,
! But they are there, and as smooth
| straight and regular as one can mag
inc. The ruling engine is kept in a. dark
chamber, underground, in dust-proof
glass case, and when in service is
guarded against temperature changes
with almost uncomfortable caution. No
| one is permitted to enter the dungeon
at such times and only a very few on
| any other occasion. Some of the most
distinguished scientists of foreign lands
have made special pilgrimage to Balti-
more for this purpose and have es-
teemed it rare privilege to be allow
ed to see the machine. The princinle
of the apparatus, however, is verv sim
pie. 1t is the exquisite workmanship
on it and the extraordinary safeguaras
employed while making it which make
it wonder. A diamond point, whose
selection occupied months of time he
cause of the need that it should possess
a certain prescribed shape, has been
mounted in tiny carriage that is driv-
en- to and fro over the mirror. The car
riage runs on set of ways or rails
and is propelled at an exceedingly uni
form speed by means Of a hydraulic
motor. After each trip the carriage is
moved a little to one side so that the
| diamond will cut its next line in a
new place. This adjustment is made
automatically, at the right instant, by
a screw which is the browning glory. of
| the whole mechanism
4 Looking for Fossils. Il
Miss Oldun-Th hat gentleman oyer
there has admired me all the evening.
Who is he? Friend a collector
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