Evening star. [volume] (Washington, D.C.) 1854-1972, 1882-12-04

ness the times both of beginning and end of the
transit When preparations were made to OBJ
serve the transit of l1el, il occurred TO an as
troao,ner, named De L;sle. that single Obser-
walton could be employed instead of two termi-
nal observations. This was an improvement
upon Haiieys method. because it diminished the
chances OF total failure, az but one contact was
necessary at each station providing that they
We're both the same. Toe transit of 1161 and
1863 were generally observed. Expeditions We're
sent to nearly every available place. Tue tran
sit of 1883 was the occasion that first took Cap
tain Cook 10 Otaheite. This transit gave more
satisfactory results than the one of 176l.
THE BLACK DROP.
in both the phenomena of the black drop. y
as it Is called observed when the critical mo-
ment of Ontact arrived. The planet had assumed
the shape of pear or balloon the elongated! por-
tioa being connected with the limb of the sun.
The result was an uncertainty sometimes
amounting to nearly a minute in observations
winch were expected to be correct within a
single second. The cause of this is apparent.
When we look at a bright cb;ect on dark
ground it looks little Larger than it really is.
owing to the encrOachmcnt of the light upon
the dark border. This encrOacbment may arise
from number of caascs-imperiections OF the
eye, mgerfectiOHs of the lenses of the telescope,
and the s0fteE;ng effects of the atmosphere.
THE MODERN METHOD OF OBSERVATION.
cussed it was seen that photography would he
valuable aid 10 the observers. but there was
much difference of opinion as to how to employ
it. Our country having finally disposed of the
question. stations We're selected and parties
dispatched. The contact observations were
first taken, but they proved little better than
those of the eighteenth century. The '.black
drop again produced confusion. and the same
rL.,i,,
vat;ons recorded TIE same phase or not. Atten-
ton was next directed TO the photographs, but
it was found that those taken by European
observers were failures Tie English thought
it best not TO publish the results of the photo
graphic observations. The American photo
graphs, however. yielded excellent
results the measurements made from them
appearing to be free from errors At recent
conference of European observers at Paris to
consider how the transit of 1882 s. C:lld b.. OBJ
served the Europeans declared the plot graphic
process Il failure. They will try the contact
method once more. The Americans know that
the Photographic method cannot be defeated by
passing clouds. and also that they can take tie
contact observations also. as they cost nothing
BY the Photographic apparatus if the sun is
visible. by using dry plates thirtv-SiX negatives
can be taken. These and other reasons lead
Americans to regard the Photographic method
as tie most efficient. The French Will use the
photograph at two out of eight stations and are
the oay ones an9ng fore IN nationsto utilize it.
There will be another conference next year at
Paris. and some concerted acton will he taken
with the view Of reducing the observations
taken Wednesday. so as to obtain the paralaX
American astronomers are stationed at
Washington, Florida. Texas. Chill. Patagonia
Cape Town and New Zealand. besides many
private persons. provided with telescopes who
will make observations. In concluding the lee
turer said this was cur last chance There will
be no other transit of Venus till June , OJ4
Not even our chiidFens children will live TO
take part in the astronomy of that day.