The Donaldsonville chief. [volume] (Donaldsonville, La.) 1871-current, 1874-06-27

The above cut is an Illustration ofVenus
coming on the SINS disc, and at A and d
it shows the two eusps. Now, if the
length of the line A p is known, and the
time at which it has this length, the time
of contact can be readily calculated. OF
course, the reverse phenomenon occurs
when the planet passes off the disc. 1t is
for the purpose of measuring these distan-
ces that the equatorial instruments are
provided, and tilar micrometers or con-
trivances. by means of which two spider
lines in the focus of the telescope may be
moved toward or away from each other.
Again observe the cut. One of these lines
is to be placed at A and the other at d.
The time will be noted, and the number of
turns and parts of the turn of a screw
which will move the lines will be noted
from the head Of the screw, which is very
finely divided. Without reference to
what methods other Governments will
adopt, at all the American stations it has
been determined that the photo hello
graph, the contact method. and the method
of cusps will be used. At the moment
when the transit comes the Chief astrono-
mer will have his station at the equatorial
instrument, and of course will observe the
first contact, and on his chronograph he
will make the record of the time, and will
Immediately commence making measures
of the distance of the cusps.
1t will be the duty of the assistant as
tronomers to see that the heliostat, the in
strument which is to throw the image of
the sun into the stationary Photographic
telescope, does its work properly, and in
the dark room of the house assigned to the
photographers they will take the negatives
just as fast as possible.
THE STATIONS.
1t may be a source of wonder to many
why the stations named have been select
ed. The explanation will be exceedingly
interesting to all intelligent readers, and
while they read the explanation it will be
well to have maps before them of the
Western and Eastern Hemispheres.
What astronomers seek in selecting sta
tons are places where the acceleration of
ingress and egress is greatest and where
retardation of ingress and egress is great
est. Now, CroZet island, the station as
signed to Lieutenant Raymond, is the
best point to observe the retarded ingress.
and so is Kerguelen Island, the station as
signed to Professor Ryan and for the ac-
CELEBRATED ingress Peking, assigned to Pro-
fessor Watson, is regarded as one of the
best. The station assigned to Professor
Peters, in New Zealand, is the best to OBJ
serve the accelerated egress, and the sta
toni in Siberia, under the care of Professor
Hall, is the best to notice the retarded
egress. With this explanation the path
way of the transit can be easily drawn.
To name a few places more easily found
on the map, the point of accelerated in
gress is near Wahoo and Hawaii, and the
point of retarded ingress near Kerguelen
Island. The point of accelerated egress
is near New Zealand and South Australia.
and the points of retarded egress near
Orsk, Suez, Bombay and Peking.
WHAT Is THE OBJECT?
What is the ultimate issue to be of all
this work What is to come from this
general attack of the nations on the prob
lem of the SUMS distance, or its ''eauato-
rial horizontal parallax," as the New
combs, Watsons, and Halls call it? This
parallax, reduced to common English. is
nothing more than an expression for the
greatest angle which would be subtended
by the earth's equatorial radius to an OBJ
server at the distance of the SUMS center.
just now there is an uncertainty in this
problem measured by some three hundred
thousand miles. It is believed that the
effort the United States is making will re-
duce- this uncertainty to at least one-third
OF its present figures. An accurate knowl-
edge of the suns distance is for the per-
lection of all lunar and planetary tables,
and all these enter directly into the science
of navigation, and through navigation
ramify and pervade the business interests
of the world.
1t is the intention of the United States to
get the best results In It's observations
and preparations made for them our Gov
eminent has not been hedged in for final
action by the precedents established in