The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1880-12-29

PROFESSOR YOUNG BEFORE MECHANICS AND
TRADEsMEN IN STEINwAY HALL.
rNew York Timesl


TRADESMEN IN STEiNWAY HALL.
New York Times.l
Professor G. A. Young delivered very
interesting lecture at Steinway Hall last
evening before the General Society Of Me-
chanics and TradesmeD, the subject being
The Moon" He began by speaking Of
the importance of that luminary, which
is mainly due 10 It's proximity to the earth,
as ii is tnus enabled to exert percepti-
bic influence upon human affairs. It is
the principal cause OF the tides 1t affects
the magnetic currents Of the earth, and
perhaps il fluences the meteorological condi-
tons 10 a scarcely appreciate degree.
It's indirect effects, however, are much
greater. The motions OF the moon first
gave to the ancieuts the idea OF moving
universe, and the earliest observations OF
astronomers were conducted upon ". BY
the records of eclipses which were recorded
centuries ago we are able TO fix the dates OF
events aud to compare the chronology of
different nations. The first recorded eclipse
was observed by the Chinese $500 years
before the Christian era, and from the year
1853 b. c. down TO the present time eclipses
have been quite carefully recorded. We
can fix the date OF Herod's death, be-
cause it IS known that an eclipse &C.
Cured on the succeeding night. The
moon furnished the first practicable
method Of finding the position Of ship at
sea. About the year IT'S prize Of CO.
900 was offered TO the first man who would
devise q method OF determining longitude
at sea within thirty miles. Observations OF
the moon afforded means TO accomplish
this result, for it was found possible TO cal
culate the position OF the moon In reference
to the stars for any hour. However, The
moon is not q very good time-indicator, for,
since it takes her thirty days to complete
the circuit, it is not possible to measure the
slight changes in her position with suffi-
cient accuracy for this purpose; it is
like using clock without minute
hand, only thirty times worse. Neyerthe-
less, in polar expeditions the moon is de.
pended upon for time, because chronome-
tiers are not trustworthy In extreme low
temperatures. Astronomy originated with
observations Of the moon, and for about a
hundred years the mathematicians and as
tron0mers were almost exclusively engaged
in studying her motions, actuated no doubt
by the desire to obtain the prize already
mentioned. Newton discovered the law Of
gravitation, but be could not have proved it
without the aid OF lunar observations. He
calculated the size Of the moons orbit, and
found that in size and form it agreed with
bis theory, for It bends In toward the earth
about one twentieth Of an inch In one see
ond.
The moon, the speaker continued, Is con.
tinuaIly getting out OF its course, or from
five to twenty minutes ahead or bebind
where theory would place it. The question
now to be solved Dy astronomers Is whether
the moon is at fault or whether some irregu-
iarity In the motion OF the earth Is the cause
of the discrepancy. The interest which IS
attached to the study OF this object is great.
Iy enhanced by the intrinsic beauty OF it's
surface as revealed by the telescope. In
this respect the most interesting OF the plane
tary bodies are the moon and Saturn. The
former is full OF variety, and constantly
changing with the direction OF the suns
light, and every increase In the power OF
the telescope reveals something new. As re-
CARDS the earth the moon Is rather an attend.
ant than satellite, for its size, as compared
with the former, is very much greater than
the proportion that exists between the
satellites OF the other planets. The lunar
month is given as 20 days, IL hours, Al
minutes, 2 seconds aud 684 1000 Of second.
The speaker would not vouch for the accu-
racy Of the fraction, but be stated that the
length OF the month is probably known to
within one-hundredth OF a second. II is
determined thus accurately by measuring
the time elapsing between two eclipses
which are separated by long intervals. The
motion OF The moon Is sdbiect to so many
variations that 10 calculate its exact posi-
tion for any given time would require
four or five hours Of steady work, and
about fifty different corrections must
be applied. This has to be done
for every hour In making the Nautical Al.
msnsc. The shortening Of the moons
month, which has been observed, is partly
caused by gradual change In the earth's
orbit, which is growing more circular. This
change will continue for about 50, 900 years
longer, after which the process VIII be re-
yersed. Laplace made this calculation, but
an error was afterward found by Adams,
which reduced bis result by about one bali.
Then the effect OF The tides was thought 10
exert sn influence by retarding the rotation
OF the Garth, but still later Investigations
have shown that the real and the theoretical
oscillations agree very perfectly, and that
the tides do not exert any appreciabIe infiu.
euce upon the rotation OF the earth.
Az Is well known, the moon always pre-.
SCENTS one side toward tho earth. We now
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