New-York tribune., 1910-09-04

finest most accurate uldCIlIiC litAot DC
made with tools and machines still finer
and more accurate. The screw cutting ma
chine first had to be graduated and made
finer than anything it could produce In
order to make machines and instruments to DO work
of an extremely nature there must be retne
ment of mechanical and methods known only to
experts These often do not pass beyond the labora-
tOrv and for that reason escape the pubic eye
Almost Perfect Screw
TAKE for instance the micrometer used to determine
the errors of divisions of angles circles, and eccen-
tries and when used at the eye end of the telescope
the astronomer can determine the position and motion
of stars and the diameter OF planets lhe screw ana
wires of the micrometer used for astronomical
observations must be fine and accurate that no
errors be detected by greatly magnityng them
MlCrometer have often one hundred threads 10
the nch and provided with graduated drums OF one
hundred divisions each, and the readings are made IN
tenths of division.
the attention of scientists for years; but while theore
cay this may be accomplished, we have for all
practical purposes secured that perfect. This
screw made by Professor Rowland IS used to operate
the greatest linear dividing engine invented The
Rowland engine is the most perfect OF all mechanss
used for ruling lines exactly parallel and equally spaced
This could be accomplished only by the perfection of
that would the cutting tool without an error
exceeding one-nlionth of an inch. Metal surfaces are
ruled with this instrument with forty-three thousand
exactly parallel lines the inch and each exactly
spaced. Speculum metal thus ruled has enabled the
physicist in his study of the spectrum to enter fields OF
research before unknown. Hundreds of specuum metal
plates either fiat curved have been ruled with
not exceeding ur-hundredthousandth OF an inch
In the construction of the mcrometer the screw IS
made perfect by mechanical means; but the cross wires
are still composed of common spider lines Platinum
spun remarkable neness; but they too
coarse for such instruments the best astronomical
micromeers The spider lines used for these cross wires
from one-fth to oneseventh of thousandth OF an
inch in diameter and these composed OF several
thousands of microscopic streams of fluid which unite
and form single line Besides their great neness, the
spider lines retain their strength and elasticity tor long
time and easily affected by changes of tempera
ture. As an illustration of this often when measuring
snspots the heat intense that the lenses OF the
micrometer eyepece cracked but the spider lines
not in the least injured.
Their durability is shown by their in the micro
of the transit instrument at the Allegheny Obser
vatory for upward of half century. The placing of
these spider lines the instruments of the most
delicate operations that experts encounter. Working
under the powerful magnfying lens with the most
and delicate of tools, they nevertheless make
which require correcting 1t is through this
bination of mechanical ingenuity and Natures finest
product that astronomers able the
Weighing Planets and Sunbeams
MEASURING the distances of stars and planets seems
AVA wonderful enough: but weighing them appears at
first thought impossibity But all this has been
compshed and The refnements of mechani-
cal have brought about great changes in weighing
methods Everything is weighed to-day. The architect
before putting up his thirty fortystory building cal
ton the al WEIGHT Of the whole mass