The evening telegraph. [volume] (Philadelphia [Pa.]) 1864-1918, 1869-09-16
THE FRANKLIN INSTITUTE.


rErominences rr,,ences and CorOnn of the Great
ECLIPSE Of August =.
The members of the Franklin Institute were treated
ieoe evening" on the occasion OF their lrst stated
meeting this fan, to the finest exhibition of photo
eoaPnic views OF solar eclipse ever given in this
whom is due the major credit for the enecve organ
izason OF the Philadelphia Photographic Expedition
70 observe the solar eclipse and the excellent mega
lives they were able to obtain-cearly explained
the construction OF the delicate apparatus made ex
preSsy dor the corps, and illustrated everything by
well-defined images castupon screen. Upon an in
side page OF The TELEGRAPH will be found ''Ecpse
N0tes, extracted from the Franklin Institute Jour-
nat which, in connection with the following outline
OF last evenings address, will give our readers an
and the hypotheses deduced therefrom. Nothing,
however, but personal inspection of the enlarged
photographs, like that given last night by the sue
cessful magnifyng OF seven distinct views taken
curing totality, can give vivid conception of the
exact and wonderful solar pictures obtained and It
Is pleasure to note that during the coming winter
season our citizens will probably be favored with
Academy of Music illustrated by profusion of
Photographic and other experiments
The Professor said:-The main point to which at
tention was directed, was the arrangement of the
Instruments for their Photographic work. 1t was a
question of much moment to decide whether they
would follow the plan adopted by the French and Ger
man expeditions OF last year, and make the photo
graph in the principal focus OF the objectgass thus
securing great intensity of light in small image or
follow the method employed by De la Rue in 1862
when he used an ordinary Hygenian eye-piece 50
placed as to produce an enlargement of the first
image from the objective. After careful study of
DE Ia Rues report and pictures, as also those OF the
later expeditions he came to the conclusion that the
plan Of enlargement presented many advantages
and should be followed with certain notifications,
which he would describe.
To the face-plate OF the camera the eyepiece tub
was attached, its other end being screwed to the
telescope. The diaphragm plate moved across the
axis of the instrument being drawn d0wnwards by
could be reduced by raising the outer end OF one or
both the upper strips so to dsengage the forks at
their end from the lower spring. and then turning
them forward In direction normal to the front OF
the box, out Of the way.
The spring was attached to the diaphragm plate by
cxuixa aI hnnl xuhia Nyhti in n fa1
out, could be detached and readJusted with the
greatest facility.
A number Of diaphragm plates were provided,
with slits respectively OF 146h, 13Oh, 12Oth, and
1-1Oth OF an inch in width. These plates could be
readily interchanged, and in combination with the
springs, gave very wide and yet delicate series of
fixed adjustments for the times of exposure.
To To n. make the exposure, the plate was drawn up
which would then retain it, On depressing the outer
end of this lever however, the hold on the pin was
dfsengaged and the plate flashed the axis of
the tube allowing the light to traverse the narrow
slit as flew past The plate was then arrested on
the end of the second lever. When an exposure of
some seconds was required during the totality,
plate having round orice exposing the entire field
OF the eye-piece was substituted for the one with
the narrow Slit and was arranged that, when
caught by the upper lever it covered the lens, but
when fallen to the second lever exposed it entirely;
when, hewever, this lever in turn touched, the
plate descended again far enough to once more
close the lens BY touching these two levers in
cession, it was then possible to make ''timc eX-
posure with great nicely and accuracy as proved by
actual experience during the eclipse.
To secure chronographic record of each expo
sure, binding screw was provided to make one con-
necton with the general mass of the face-plate in
Guiding the lower and upper levers, to carry on the
circuit when the downward motion OF the lever
point projecting. In raising the lever for new ex-
posure the spring at its side was pressed back so as
tai break-pece would have been made had time al
lowed, but this was found to operate in perfectly
AS the operation OF the eye piece, when employed
to produce an image on the screen or ground glass
of a camera is essentially different from that which
Mr.. Zentmayer to make some alterations in its form.
Thus, in the first place. since in the present the
"eye-lens' of the eye-piece undoubtedly makes
secondary image of the primary image formed within
tive and the e Id lens of the eye-plece it is clearly
desirable to make this lens of a longer focus than
Usual, that its errors may be of less account. 1t
was also essential to give the new eye-plece wide
angle, as to secure sufficient field not only for
the solar Disc but also for the corona.
The reticule mounted on short tube, with
fine thread on the outside running in corresponding
approximately adjusted beforehand, moved to
its exact place by turning it with a sharp point
1t was found by experiments made previous to
starting, that with clear sun, it was necessary to
reduce the aperture OF this telescope (Which was
inches, with so inches focus) to ~ inches, and to
all three springs and the diaphragmslide of lao
inch aperture, IN order to get prop proper exposure 1
diameter at the principal focus OF the obectlve) to
21G inches on the ground glass The same size of
during the partial phases, the entire aperture, in all
cases. of course being'used during totaty.
"A
lard at this time, in photographing the moon which
were OF great value in settling the time OF exposure
which would probably be required in the total phase.
He found thai good impression could be obtained
of the full moon in about one minute, and that an
abundantly strong could be secured with an eX-
posure of three minutes. From this and the deduc
tOns of De la Rue, that the gh OF the prOminences
1870 times as great as that OF the full m0on 1t
appeared that exposure Of from one-third OF o
second to one second, during totaltty, would have
been sufficient to secure images of these bodies
For the corona OF course much longer exposure
would be required; put no estlmate could be made
as to what would be its duration.
At the Burlington station, Photographic record
of the fret contact was secured, by exposing plates,
in rapid succession, about the calculated time. A
very good result was thus obtained AT Mount
Pleasant, we placed plate ready in the camera and
then waited signal from Professor Watts n, OF the
University OF Michigan whQ with his party, was on
the ground with us, and was watching for the tirss
contact We thus obtained a picture showing q very
slight ndentaton. By measurement OF this, the time
of actual first contact be reached by calculation
yet more precisely than would be possible with any
eve observation.
During the partial phases, accurately timed expo
sures were made by all parties. The slide making
the exposure had aperture OF only lOth OF an lnch
while the time OF exposure Is mecnannlcally SHOWN
TO have been but 1900 OF second. The delicate
mechanism used for this end, already partially de-
scrbed worked several recording pens OF the Morse
instrument. An electric discharge was passed from
the brass plate of the slide through the trigger at the
instant OF its fall for an exposure and was then re-
~ corded as dot on moving slip OF paper similar
connection with chronometer Indicated In dots on
the same sliD each second OF time; thus IL was only
n matter OF careful measurement to ascertain the
time and length OF each negative -
The partial-phase pictures show the various sum
spots visible at the time about six In numoer) with
admirable definition, the larger ones being sur
rounded by q marked fringe OF faculse, and give
also distinct granulation over the general SURFACE
of the sun. Two OF these large sun-spots are about
5000 miles in diameter, big enough TO allow our gloot
nhau oil Increase