The morning news. [volume] (Savannah, Ga.) 1887-1900, 1894-11-10

thirty-ive miles a second.
To-day between the hsurs Of 10 ana 3
oclsck the planet Mercury win make
transit across the disk OF the sun. and
the following computations of the phe-
nomenon have been made specially for
the Morning News. and adapted to the
latitude and longitude Of Savannah in
city time:
h. m. $.
First conts ct................1o 81 % a. m.
Middle OF transit. ........... u p. m.
Last contact. AZ 43 p. m.
The first contact occurs on the eastern
limb OF the sun IS degrees 80 minutes
from the north point and the last con-
tact on the western limb 40 degrees Al
minutes from the north point 1t will be
thus seen that the path of the planet
will be almost directly across the suns
greatest diameter, and for this reason 1t
is of more than usual interest.
Although Mercury is 1900 miles in diam
eter its distance from US is so great that
it will scarcely be visible to the unaided
eye. Still a telescope Of moderate power
will reveal it as a small black spot slowly
crossing the disk of the sun.
The planet Mercury revolves around the
sun in about lightweight days at a mean
distance of 5000, 600 miles, and the earth
makes a revolution in about 565 days
at a distance of 5000 600 miles. Mercury,
therefore, sometimes comes between us
and the sun when it appears TO cross the
suns disk as small, black spot. This
is called a transit. Now, Mercury makes
a complete revolution around the sun and
catches up with the earth again every 116
days, and it would seem, therefore, that
we should have a transit at every synodic
period period of ZIG days. This, indeed,
would be the case if the orbits of Mercury
DH ~ ri cd N ba q
plane, but the orbit of Mercury is inclined
or tilted about degrees from the plane Of
the earths orbit, intersecting it at two
points called the nodes. A transit is i'm
possible, therefore, at any point except
at or near the nodes, and both the earth
and Mercury must pass the node at the
same time. At all other points Of the
orbit Mercury, at inferior conjunction,
passes a little above or below the sun,
thus missing a transit. Now, ffty-four
revolutions of Mercury are nearly equal
to thirteen revolutions of the earth, and
hence, when a transit has occurred at on9
node, after an interval Of thirteen years,
the earth and Mercury will return to
nearly the same relative situation in the
heavens, and another transit may occur.
Transits may sometimes occur at the
same node at intervals of seven years,
and transit at either node is generally
preceded or followed at an interval of
three and a half years by one at the other
node. Thus the last transit Of Mercury
occurred on May 8, 1891, and the next will
take place ON Nov. 4, 1901
The transit of an inferior planet affords
the best means for determining the dis
lance to the sun, and although the transits
of mercury are far less valuable for this
purpose than those of Venus, the greater
frequency of the former gives them much
Importance. A transit of Nenus is a very
rare phenomenon, the next one occurring
on June in the year 2004
But the chief value of the transts Of
Mercury lies in the application, of the
data derived from them in the solution OF
a question which has long been unsettled
in the minds of astronomers, that of the
uniformity of the earth's rotation upon Its
axis. There are theoretical grounds fol-
thinking that the time of the earth's aka
| rotation, and Consequently the length Of
the day, is slowly changing. The friction
! of the tides has a tendency slightly to re
! tard this motion and hence to lengther
| the day, while on the other hand the cool
! ing and shrinking of the earth has just the
! opposite effect.
A few years ago Prof. Newcombe a dis
! tinguished American astronomer, under
| took an investigation of all the observed
transits of Mercury in historic times will
a view of ascertaining if possible whether
! or not the length of the day is changing
After a most exhaustive analysis of all thu
data at his command the result showed
| that there has been no change in tn,
length of the day. The two forces abov,
mentioned, seem to compensate each other
It is afact worth noting that in all the uni
verse the only uniform motion known Il
astronomers is the rotation of plane
upon its axis.
Mercury is now near its perihelion and /
moving at the rate of thirty-fiVe miles
| second.
1t is difficult to realize that the small
black dot upon the sun to-day is plane
5000 miles in diameter and moreover tina
while it appears to be nearly stationary
is in reality moving one hundred times a
fast as cannon ball in it's swiftest flight
ASky