New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1897-03-07
4 WONDERFUL MACHINE.
1T ENGRAvEs HUNDRED THOUSAND
LINES TO THE INCH

| IT ENGRAVES A HUNDRED THOCsAN
LINES TO THE INCH
The announcement was made a few days ago
| that large ''dTracton grating" spectroscope hao
| lust been finished al the shops OF John a. Brash-
| ear In Allegheny Penn. for a German astronomer
This calls fresh attention 10 unique almost
unknown and remarkable piece Of machinery the
ruling engine Of Professor Henry A. Rowland. Oh
Johns Hopkins University. wherewith an important
| part Of the instrument just mentioned was made.
| The object OF spectroscope Is to anaiyze hsht
from a star. a nebula. the some other urni-
nous object In this operation the image OF mar
slit H. expanded sideways until II IL converted
into u long prsmatic band or spectrum. violet AZ
| one end ard red AT the other. For studying most
Of the heavenly bodies. glass wedges or prisms are
employed 10 perform the work These properly ar
ranged will render good service, where high
dispersion magnification. Is not desirable
But with the sum- whose light IL so intense that II
will stand great diluticn $50 10 speak,. far more
cons;dera Bile disperx,on is entirely feasible And
the astronomical spectroscopist Is anxious 10 pro-
duce this effect, In order more completely to sep
arae cross lines in the spectrum. which are ordi-
nary too close together to be properly distin-
guished The whole point Of certain researches de-
ponds altogether on the possibility Of identifying
suspected line positively and Of measuring It's po
sition In the spectrum with precision. Such sep
araon can be much better obtained with graf
ing than with prism.
There are two kinds Of gratings One consists OF
glass. whose surface a series of fine. parallel
lines ruled. TIE other IS highly polished
metal plate. similarly engraved. The former lets
the light shine through It: the later reflects II. In
either case the effect Is TO produce a spectrum
actly prism does. To the metal plate a slight
concavty is previously impaired. that IT Will
focus the image without the OF lens
II Is this latter type of grating which intro
duced into the new spectroscope Brashear made
the mirror. gave IL just enough curvature 10 make
| the focal distance twenty odd feet and then
sent 1t 10 Baltimore for treatment in Professor
ROwland's laboratory
IL IL stated doubt with truth that the lines CT
this particular grating fine and SO close
together that there 10000 the inch. A SIM
pie comparison Will enable one easily TO realize
"hat TINS means In the majority of books there
are from 200 10 go leaves TO the inch when the
covers are pressed firmly together In a small
minority. the number Will range from 800 TO go
These latter figures represent rather thin paper
Now, If we could split Of the very thinnest OF
these leaves into 800 layers OF uniform thickness
the product would be equivalent 70 1880 TO the
men, or a little less than the number of lines in
this specttoscope grating. 1t must be RENE mberad
moreover. that there must be little space between
the lines II one is be distinct from the other
Therefore. If inch be divided up into 100000
equal parts. nine Of them would be covered by a
line and space II Is stated in one of the ne US
dispatches that the space 3.C0O00ths wide:
from which II must be inferred that the line was
scco,oonhs Of an inch wide, OF cours. II is
impossible 10 See such lines with the naked eye
Only d very powerful microscope would reveal
them But they are there and as smooth straight
and Tegu ar as one can imagine.
,,n Inc rumns engine is kept in dark chamber
In service Is guarded against temperature changes
with almost uncomfortable caution. No one is per.
United 10 enter the dungeon at such times and
only very few any other occasion some OF
the most distinguished scientists OF foreign lands
have made special pilgrimage to Baltimore for
TO be allowed 10 see the machine. The principle
OF the apparatus. however. Is very simple II is
the exquisite workmanship OIL ii. and the extraor-
binary safeguards employed while making H.
which make it wonder diamond point
whose selection occupied months OF time because
of the need that II should possess a certain pre-
that is driven 10 and fro the mirror The car
rage of ways or rails and is nro
PEELED at an exceedingly uniform speed by means
OF hydraulic motor After each trip he car
riage is moved a little TO one side so that the dia
mond VIII cut It's next line in a place This
adjustment Is made automatically. at the right in
the whole mechanism II is the perfection OF ac.
curacy The remains motioniass Will. a line
Is being engraved. is then turned small fraction
of revolution by gearing. and again keeps still
while the diamond is AT work II will be readily
understood that by multiplying the gear TO the
right degree. and having one tooth OF the fastest
lines to the inch can be raised to any degree con-
sistent with the possibilities of the grazing TOOL
In several OF the best gratnss in use there
only from 10000 90 010 lines to the inch RIO on
stances One instrument In which the ruling had
this degree OF fineness was completed about two
Dublin Another was ordered for Magili Univer.
sity in Montreal The one lust finished is TO 20 70
Hans Hausawaldt. OF Maedeburg. who il described
In the papers as IA wealthy scientist"