Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1874-11-04

not appear that there was much i'm
provement on the estimate made by
Cassini century and half BEFORE
viz: that it was not less than IS, 900,
900 miles.
The records of observations were
scrutinized and weighed, and the cal
culations based upon them repeated and
criticized, The great Encke, in 1924,
after several years of special study of
them, summed all up and gave as the
best result attainable 1924 900 miles.
The scientific world, hopeless OF any
thing better, seemed for a time to &C
quiesce, as there could be no sensible
doubt Of it's accuracy.
But its accuracy has since been i'm
plunged, and on very strong grounds.
1t was known that light travels from
the sun to the earth in 8 minutes Is
seconds. Experiments carefully made
by Arago, Foucault, and Fizerau, show
that light travels at the rate of 1876, 900
miles per second. This would give
the distance of about 81 10000 miles.
LIE Verrier, the discoverer of the plan
ct Neptune, and Mr.. Stone, made it
81, 100000 while Hansen the Dane
found it 81, $3.50, 900 miles.
This is the position of the question
now, and our astronomers aim to obtain
yet more precise and definite result.
Will they succeed? They are full of
confidence now. What will they say a
year hence? Time, learning, skill, en-
ergy, money, everything that man can
give, will be devoted to ensure success
in the astronomical work to be done on
the 9Th of December next.
The astronomers will follow two
methods, known as that of Haley and
Delisle. They each require two sta
tons, so far apart on the surface of the
earth as to give satisfactory base line.
In fact the farther apart the better, all
things else being equal. For Halley's
method, the two stations lie as nearly
north and south as may be. For De-
isles they lie east and west.
Let US suppose two stations to be
chosen, on or nearly on the same me-
ridian of longitude, and 5000 miles
apart From each of these places the
planet is seen to traverse the disk of
the sun, like dark spot moving stead
lily across an illuminated dial-plate.
The lines as seen so far apart are sensi-
bly, different What the observers first
seek to know is the apparent distance
between these lines, and the angle they
form when seen from the earth. Were
both seen at once from the same sta
ton, with the same telescope, it would
not be difficult for skilful observer to
measure the angle directly but at each
station only one line is seen, if indeed
we may give that name to the course
of the black spot that passes on and
leaves no trace behind.
Each observer must determine the
correct position of his line across the
face Of the sun, in order that it may be
afterwards compared with the other
line similarly determined by calcula-
ton.
The English observers are now as
sembled at the Greenwich Observatory
in London, undergoing a course OF
training for the grand day. They have
a FAC-SIMILE Of the sun and Venus,
which are made to move in such man
ner as to give as exact representation
of the transit as possible, and they
practice observations on this artificial
transit 1t is said that even in this
facsimile the black band has shown
itself, and that one important lesson
now being learned is how to Judge of
the instant of contact despite this OBJ
stacle
There is, however, another and still
better safeguard-the use of photogra-
ply. The transit will record itself
more minutely and more accurately
than any other observations for meas
urement could do. The stereoscope
comes In also, to- aid in determining
with the utmost precision the moment
OF contact.
It is confidently expected that by
some one or BY all of these methods
the mistakes Of 1851 and of 1859 will
be avoided, and that the instants of the
commencement and conclusion Of each
line Of the transit may be so accurately
determined that for neither Of them
will the error Of their duration exceed
one second.
Did the time occupied by Venus in
making the transit, as seen at one sta
ton, differ from the time as seen at the
other by on y one minute, the uncer-
tainty would be less than two per cent,
bat in fact the times will differ by Is
minutes, and by skillfully choosing the
places difference of twenty minutes
may be obtained in that case the error
or uncertainty would be less than one
per cent. For the present, the scier.