The morning call., 1895-01-31

his method in the Photographic Times as fol-
lows:
81 shall assume the latitude as known.
shall also assume the local time as known ac
curately within few seconds, for this may be
found with the same instrument with which
the latitude is determined.
"The moon may be regarded as the hand OF
a gigantic clock, round the face of which she
moves once month. The face of the clock
carries no numbers, but it is covered instead
with innumerable luminous specks, whose posi-
tons are accurately known, so that the exact
position of the hand with respect to the specks
gives the determination of time. But to deter
mine it accurately something else is required.
The hand of the clock is not near the face, but
a long way off. Therefore two spectators in dis
ferent places of the earth do not at the same
moment see the hand exactly in the same posi-
ton ON the face. They must take account of
this when determining time, and they do it by
calculating where spectator would see the
moon who could observe her from the center
of the earth. To calculate this rough knowl-
edge of their position on the earth is suff-
cient.
1.-THE time thus determined by the position
of the moon is a universal time common to all
inhabitants of the earth. We may deduce
Greenwich time from it if we make use OF a
nautical almanac, where the position of the
moon is given for every hour of Greenwich
time, and may easily be calculated for any mo-
ment in between. If now we know our local
time, we can from the difference between this
and Greenwich time tell our longitude. Four
minutes difference corresponds to one degree
difference in longitude. East of Greenwich the
local time is in advance of Greenwich time,
west of Greenwich it is behind.
"The moon moves very slowly, $50 degrees
in about thirty days-that Is, half degree in
an hour. Therefore, to find Greenwich time
with an accuracy of one minute would require
to determine the position of the moon with an
accuracy of the 120th part of degree, or of 80
angular seconds With sextant you want
some skill to measure an angle as accurately
as that But by means of an ordinary camera,
of say "a centimeters (about 10 inches) focal
length and good lens, you would require very
little practice to be able to take a photograph
from.which Greenwich time may be deduced
with an accuracy about FIVE times as great.
~ shall describe the way proceeded. di-
rected the lens to the ms.bn, focused the image
as nicely as possible, and propped the camera
up with books so that it kept its position unal-
tered. Then 1 took number of almost instan-
taneous photographs of the moon ON the same
pate, removing the cap about every two min
did not use an ordinary cap, but only removed
a piece of black velvet that was placed little
distance before the lens, because 1 was afraid
of altering the position of the camera by touch
ing it. / carefully noted the time according to
my watch, corresponding to the exposures. If
on this photograph one could see number of
stars near the moon, the time might be read off.
But with an ordinary lens, only bright stars
would appear, which do not happen to be near
the moon often. So had to proceed somewhat
differently. left the camera alone until the
moon had passed, and then 1 removed the cap
and left the plate exposed for two hours, only
interrupting the exposure about every five or
ten minutes for only five seconds and carefully
noting the time of the Interruptions. On de-
veloping the picture given herewith appeared.
'The interruptions in the trails caused by
closing the lens for five seconds have been ex-
aggerated in the cut. In the plate they are so
small that they can scarcely be seen with the
naked eye, but they appear quite distinctly
under the microscope, except where the stars
approach the horizon could easily find out
which stars the trails correspondent to. For the
brighter ones there was scarcely an alternative,
as I knew the region of the celestial globe
where had to look. And having found two, L
could, by exactly measuring the distance of
their trails. and the distance between these
and the finer trails, calculate the polar distance
of these very accurately, and find the CORE
spending stars by help of star catalogue. BY
measuring the position of the Interruptions on
the trail of one star with respect to the inter-
ruptions on the trails of two other known stars
I could also tell how much it was in advance
or behind either of the two; that is to say, how
much earlier or later it must have passed the
meridian Now had TO measure the position
of the moon pictures with respect to the trails
and Interruptions. - From the position
OF each picture 1 calculated Greenwich mean
time OF the moment the picture was taken in
the way have roughly explained"
Apropos of Sibyl Sanderson's appearance and
great success in New York, the Sun prints the
following letter written some time ago by
Massenet about his famous pupil:
H. Louis Lombard, Director Conservatory of
Music, Utica, NJ T.: l love your great country.
To it owe my greatest theatrical success, 'Es-
clarmonde."
l owe it to the unique, Incompatible artist
who has created the role. / owe it to an Amer
lean, to Miss sibyl Sanderson of San Francisco.
On Thursday, the one hundredth performance
of "Esclarmonde" took place in Paris; the one
hundredth performance of Miss Sibyl Sanderson
without one day of rest. The fact has never
before existed. And what rolel
This young girl has an extraordinary voice;