The morning call. [volume] (San Francisco [Calif.]) 1878-1895, 1892-01-24
A COMPENSATING
SCREW PERFECTED.
The Machine Constructed by a Johns
Hopkins Professor.
A Million Lines to the Inch - Scientists En-
abled to Study Accurately the Spectrum
of he Sun and Other Matters.

After he shall have fitted this TO its new
bearings and made other changes in the
third dividing engine that he is construct
ing he will have, says the Baltimore Ameri-
can, the most nearly perfect machine in the
world, and, in many respects, the most Won
derful that has ever existed. With these
machines he makes the grating" with its
myriads of lines drawn regularly across it,,
by means of which he and other scientists
of the world are enabled to study accurately
the spectrum of the sun and to determine
what elements known to us are there and
to unraYel other mysteries about the nature
of the great luminary, as also to learn the
composition and distance Of other stars in
the armament
Many years ago Professor Rowland dis
covered how to make the perfect screw,
which he has described at length in "Ency-
clOr@dia Britannica" This screw is neither
the cutting screw of the carpenter or of the
iron-wOrker, nor the thread screw of the
commonplace nut. but the screw Of mechan-
les. device for applying mechanical power,
the action of which is best known in the
wheel and axle. This screw which Profess
sor Rowland has been making has spiral
ridges, like any other screw, and its UrinCi-
regularity and eVenness In running his d.
Vidng engine.
Tire new screw, which has been the sub
lect or SO much experiment by the great
scientist, and whose Improvements are the
result of the close study of certain unSatls-
factory experiences, is of steel. The last
one was of BesSemer steel, which, it was
thought, combined both the requisite soft
ness and homOgeneity. But for 4 new one,
JesSup's tool steel, annealed at the factory,
has been found to have the required fine
grain and the SOftness, and to be far more
perfectly homogeneous than those previously
made. 1t was cut Ill the workshop OF the
physical laboratory OF the Johns Hop
kluS on
AN ORDINARY LATHE,
And thereafter ground with fine emery
under water and OIL maintained at a certain
temperature for over three weeks. Over its
entire lie 9Th was placed nut ground as
nearly perfect as possible, and this was
moved to and fro constantly. IL the threads
were not exactly even at the one end or at
the groove, the pulling Of the machine
against it wore it down. So that after this
long grinding each of the screws has been
made 10 ut almost exactly over each other,
and thus each has compensated for the i'm
PROJECTIONS of the other. The screw IA
inches III diameter, Is II inches long and has
threads - 10 the inch. In the dividing ell
gine in which this is to be placed, despite
the peTfectitude Of this screw. there is in
trOduced periodic error, due 10 the cOgs ar
TanRement, and this Professor Rowland has
arranged 10 compensate for
Every precautCn is taken TO have this the
most perfect Of the dividing engines, which
Professor Rowland has devised to do perfect
work. In the Sub-cellar of tie physical
laboratory, where tie travel in the neigh
boring streets cannot shake it in the least,
the vault is so placed that its temperature
a m
pOrtant consideration in ruling the fine
lines. The motive power is water, which
fails evenly from a tank always kept at the
same level. 1t is on the roof. The water
drops into q well-prOtected miniature tur-
biuc wheel in the basement, in which there
are cOmpensating devices to make it rule
regularly. The case supporting the Won
deriul little engine in the vault beneath is
OF iron, 200 pounds IN weight, and its bear
ings are OF steel or brass, which have been
found to work we'll when swathed in Oil.
To show with what nicely the machine
has been made to run, the professor says
that its work was not salts factory for nearly
year, because the proper oil was not used.
Now sperm oil mixed with kerosene is used
on sOmo parts and only the sperm oil on
others, and 1t IS found to get along all right.
The cutting of Tie very fine and closely
ruled lines are done by a diamond. 1t takes
up most OF the time of the master mechanic,
Schneider, to cut and set this crystalline
ruler, and the machine has to be run hun
dTedS Of times before 10 is known the point
VIII do its work we'll and will assist in put
ting each line in
ITS PROPER FUNCTION
An indispensable condition for the success
of the machine. This cutting edge is to be
supported In the new apparatus under con-
StructlOn, not on sliding carriage, but by
q pendulum arrangement. The diamond is
on The end of a little lever, which rests by
its own weight on the surface to be ruled.
The lever is attached to a sliding carriage
whce moves back and forth. drawing the
line as it goes forward and rising 0 itself as
it reCedes. AS it is going back the carriage
Is moved forward automatically by the sper-
feet screw by the amount corresponding TO
one notch in the divided head Of the screw,
the power from the water wheel being indi-
rectly applied by cam arrangement.
As there are 1000 nOtches in the head and
90 threads to the inch, the movement for
ward by this setting OF the machine is one
twenty thousandth part Of an inch, so that
the machine makes about 500 lines an hour,
and, therefore, 19. 200 lines in twenty-four
hours, without being touched, for to do so
would spoil one OF the valuable plates being
ruled. The ruling is done on highly pol
ished Speculum metal, such as is used 10
line the barrels Of telescopes. twas found
that glass and many otherwise suitably
polished surfaces wear out the diamond too
rapidly.
The screw, although nearly perfect intro
duced into the ruling of the lines constant
error. which varies regularly. This is due
to the errors in the graduation CT the head
OF the screw, and with other causes cOnsti-
tuted for long time a difficulty which
could not be well dealt with. The meaning
of the error will he appreciated from the
statement that one like this Of a milionth Of
an inch affects the spectrum seriously.
Professor Rowland has, however, devised,
q complicated arrangement to cOmpen-
safe for this error. 1t is g system of levers,
which move q bar against which the nut
rests TO prevent its turning. As the machine
moves forward the nut tends to turn with
it, and this bar is to prevent its doing so.
The method Of making and grinding the
screw, of mounting the cartridge and nut and
of cOmpenSatiEg for the periodic error are
all of Professor R0wland's devising.
The machine is capable Of ruling 900, 900
lines to the inch with ease, but the eye
could not detect them, as even with the
strongest microscope only upward of 100000
lines to the inch can be distinguished. The
largest grating made, about five inches in
diameter,
CONTAINS ABOUT 10000 LINES,
ABOUT the number which the professor finds
best suited for the research work, for which
they are intended. Such a grating takes
six days and nights constant ruling to make
And 1t is very bard to make one. Since
June the professor and his assistant, Mr.
Schneider. have been trying in vain to rule
II perfect one for Professor HelmholtZ, the
great German physicist. Such grating"
as it is called, is rare, and is worth over
$500 and even that brings no profit to the
university. Since the machine was first
made. in 1882, about 1000 have been made.
every prominent physicist in the world who
uses a spectrOScOpe having one of them.
Other scientists have made such gratings,
but the lines have not been drawn regu-
larry on them. Of the small sizes. nine out
of every ten are good. but of the larger ones,
especially the cOncave gratings of Professor
Rowland'S invention for the more important
kinds Of WORK, not more than one in five is
good.