The Lamar register., 1897-10-30

fresh attention TO
unique, almost unknown and re-
markabIe piece of machinery, the rul-
ing engine of professor of Johns Hop
kins 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 star.
a nebula. 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.
prismatic 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
to perform the work These, properly
arranged. will render good service
where a high dispersion" or magnifi-
cation Is not desirable But with the
sun. whose light is so intense that 1t
will stand great dilution $50 to speak).
a Tar 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,
which are ordinarily too close together
to be properly distinguished. The
whole point of certain researches de-
pends altogether on the possibility of
Identifying suspected line positively
and OF measuring Its position In the
spectrum with precision. Such separa-
ton can be much better obtained with
a grating" than with a prism. There
are two kinds OF gratlngs. One con-
sists of glass, on whose surface a se-
ries Of fine, parallel lines are ruled. The
other Is highly polished metal plate.
similarly engraved. The former lets the
light shine through II; the latter re-
hects II. In either case the effect is
to produce a spectrum exactly as a
prism does. To the metal plate a slight
coneayity is previously impaired, so
that 1t will focus the image without
use OF an extra lens. II Is the latter
type of grating which was now intro
dueed into the new spectroscope. Bras
hear made the mirror. gave 1t Just
enough curvature to make the focal dis
tance some twenty-odd feet, and then
sent II to Baltimore for treatment in a
laboratory there. II is stated. no doubt
with truth, that the lines on this par
ticular 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-
ber will range from 300 to $50. These
latter figures represent rather thin pa
per. Now. II we could split one of the
very thinnest of these leaves into 800
layers OF uniform thickness. the pro-
duct would be equivalent to los, 900 to
the inch, or little less than the num-
Der of Inns in this spectroscope graf
ing. 1t must be remembered, more
over. that there must be a little space
between the lines II one is to be dis
tinct from the other Therefore, IL an
inch be divided up into 1000 900 equal
parts. nine of them would be covered
by line and space. It is stated in
one Of the news dispatches that the
space was 5000, ,ooOths wide: from
which 1t must be inferred that the line
was 5000. .O00ths of an inch wide. OF
course 1t is impossible to see such lines
with the naked eye. Only a very pow
erful microscope would reveal them.
a.