Delaware gazette and state journal. (Wilmington, Del.) 1883-1902, 1891-09-10
MIL MEASURE s7,AR prscs.
Remarkable Work Done in the Fine Air
of MT. Hamilton.
SIM Erunciacai IL Ir,ur

San Francisco Examiner.
| During the last week or so the as
tronomers at the Lick observatory have
been struggling with the problem OF
measuring heavenly bodies that are in
visible to the naked eye, and thst even
through the telescope seem hardly more
than mere points Of light.
The experiments have been conducted
under the direction of Professor A. A.
Nicholson of the Clark University, who
has designed continuance and new
system that makes this sort of work
possible.
The satellites of Jupiter were taken
as subjects to experiment on. Through
the telescope ordinarily these appear
like bright dots surrounded by faint
circles of light, called interference
fringes." The edges of these moons are
so vague that the measurements hereto
fore attempted were very unsatisfac-
tory. The results of the measurements
for two successive nights have varied as
much as 1000 miles--and that is much
when it is considered that the largest of
the moons of Jupiter is not more than
5000 miles in diameter
The new plan is 10 cover the lens of
the telescope, leaving two narrow Sits
to see through. These Sits are moved
by delicate system of screws, and while
the observer watches the star he is
measuring he moves the Sits very slowly
further and further apart. When the
distance between the Sits reaches a GER
tain point the interference fringes"
disappear from the object. When this
happens the distance between the Sits
is measured. This distance bears di-
rect relation to the size of the object to
be measured, and from 1t they figure
out the angle. This found and the
distance of the object being known, 1t
is simple mathematical proposition to
find the diameter OF the star, satellite or
planet.
That is what they did with the satel-
lites of Jupiter. -Four nights In success
sion they measured the four satellites,
and the results varied but 1 or 2 per
cent each night That means that the
various measurements of the diameters
agreed within about so miles. By the
old system of measurements the results
differed from night to night 10 and even
90 per cent.
The average measurements of the
angles OF the four satellites by the old
system We're LOS seconds, 81 seconds,
1.54 seconds and 1928 seconds. The
averages by the new methods were 1.04,
.98, LAO and 1,34 seconds.
The astronomers are enthusiastic over
the success Of the experiments, particu-
larly as an attempt to perform them at
the Harvard Observatory failed. Prof.
Nicholson returns to the East to-day,
and will send out an apparatus that can
be applied to the big telescope.
These experiments were tried only
with six-inch lens. Applied to the
36-inch lens, much greater results are
expected. With it they will be able to
measure points only one.sixth the size
of Jupiter's moons. The fixed stars
that it has heretofore been considered
impossible to measure will have their
dimensions taken down.
"Why," said one of the astronomers
yesterday, tive will be able to measure
accurately stars no bigger than our own
sun |"
These are the first practical tests of
the new appliance, Professor Nicholson
found his system worked in the labor
atory, where he measured minute holes
in cards, &c, until the theory was thor
oughly tested. 1t was feared that the at
mospheric disturbances, due to refrac-
ton, would prevent tho success of the
plan when it came to measuring stars.
Ii was this trouble that spoiled the ex-
periments at Harvard,
When the apparatus for the big telc-
scope comes out it will be first tried on
the satellites Of Saturn, which are much
smaller than those OF Jupiter. Then
some of the asteroids, minor planets
that are only visible through the most
powerful telescopes, will be observed.
The experiments on Mount Hamilton
were extremely successful, and scientists
are enthusiastic over the prospective re-
suits, which they say arc of great i'm
portance to astronomy.