Evening star. [volume] (Washington, D.C.) 1854-1972, 1882-03-04

az Ingenious parts of the whole continuance
The plate-hOlder is brass frame, seven inches
square on the inside. revolving on a vertical
rod, which passes through the iron plate on top
OF the pier. Into the frame is cemented q square
Of plate glass which is crossed and recrossed by
large number of very fine etched lines. dividing
the glass into small squares The sensitive
plate goes into the other side of the Frame and
tne me r9ied lines are photographed upon every
picture of the sun taken. and provide the means
OF detecting defects in the photograph that
might otherwise go unobserved. Through q
perfOration in the center of the frame is sus-
pended plumb line of fine silver wire. This
line Is also photographed and makes true YER
tcal line on the plate. spirit level on top ofthe
frame being consulted in arranging the appa-
ratus. As the object glass and the Photographic
plate are on the same level, and in the meridian
OF the transit instrument. by which the time ia
determined, the image of the plumb line on Che
photograph makes permanent record Of the
meridian.
THE OBSERVATIONS IN DECEMBER.
These instruments produced such satisfactory
results that the commission have decided to use
them again at the coming transit. The, great
confusion caused among European astronomers
oy the lack of uniformity in their methods and
the imperfect apparatus used. has, it appears,
created a prejudice among them against photo
graphic apparati, and they will discard them
next December. On the other hand the men,
bers of the American commission are confident
of success. One of these gentlemen, talking to
STAR reporter said. he believed, that observa
tlOns taken by the American method would
ultimately be depended upon for determining
the solar parallax.
WHERE THE TRANSIT WILL BE VISIBLE.
The region of visibility of the transit of next
December will include the whole American con :
tlnent, except some portions in or near the
Arctic Circle. The beginning will be visible
over large part of Africa and the end over
most of the Pacific ocean.
ADMIRAL RODGERS VIEWS
With the papers sent to Congress by the Pre-
sldent last Tuesday concerning the proposed OBJ
servations Of the transit Of Venus was the fol-
lowing letter from Admiral Rodgers, Superin-
tendent Of the Naval Observatory, to the Secre-
tary of the Navy:
II have the honor to inclose herewith bill
which it is proposed to offer to Congress in order
to obtain the means Of observing the transit of
venus. which will occur on the 9th of Deem
Der, 1882. The transit of Venus is regarded by
astronomers as an important means of obtain
ing the parallax of the sun-a quantity which
enters directly, and as most important factor,
In the deductions of astronomical science for by
its parallax our distance from the sun is COM
puted, and our distance from the sun ia the
unit by which the universe is measured. The
English government in 1869 sent out
Captain Cook to observe the transit of
Venus, whence resulted the discoveries of
that ilustrious navigator which have so much
redOunded to the honor and to the advantage of
Great Britain. In these days, the importance
of the transit of Venus has become relatively
less since other means Of finding the suns par
allax have been devised; but the transit of
Venus is still of so much moment that the coun-
tries of Europe are already making extensive
and costly preparations to observe the transit of
December next. We cannot afford to neglect
this One which will be the last until the year
2OO4. The principal instrument employed by
ourselves is different from anything which
it is proposed to use in EurOpe-in contem-
plating to use the horizontal to-heliograph
This method is peculiarly American, and its use
seems to promise so well that We think it should
not be neglected. Foreign Photographic meth
obs have apparently given no results of value
1t is deemed important that the instruments
already on hand should be overhauled and put
in order, SINCE when the regular appropriation
is made, time will not serve to prepare them
TO this end ask that the accompanying papers
be forwarded to the honorable chairman of the
Senate committee on appropriations in order
that the sum of $4,000 for the preparation and
repair of instruments, and for preliminary ex-
perments, may be made available during the cir