New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1883-07-01
SCIENCE FOR THE PEOPLE.
TIE GREAT sTREAKs IN THE MOON.

TIE GREAT STREAKS IN THE MOON.
The moou's face, says Mr.. Richard A. Proc |
TOR. reiis ms of remote youth--a time of fiery |
activity, when volcanic action even more effect
i've Though not probably more energetic) than
any which has ever taken place on TINS globe,
tupheaved the moons crust. But SO soon as we
consider carefully the features or her SURFACE
we acc that there must have been three we'll
marked erss of vulcanian activity. Look at the
muliituduous crateTs, for example, around
the Metropolitan Crater Tycho. They tell us
OF century after century of volcanic disturb
ance-but they tell us more They mark a
surface which varies in texture, and therefore
in light.refecting power IN such way as 10
show that the variations were produced long
before the volcanic action began by which the
craters were formed. For the variations of
texture are such as to mark series OF stTeaks
some OF them two or three Thousand miles In
length, and many miles in breadth, extending
radislly from fycho. CrateIs lie indiuerehtIy
on these brighter streaks and on the interven-
ing darker spaces, and some craters can De
seen which lie right across bright streak WIN
parts of their ring on the darker regions ON
both sides OF the streak VI course thls proves
that the craters were formed long after the
great streaks.
When the streaked surface was formed,
it must have beea toeraby smootn;, Tor
we see the streaks best under tuli lliumis
nation, and there is no sign of any difference OF
elevation between them and the darker ground
all around they are neither long ridges nor
long valleys, but mere surface markings.
Yet must they have been formed 10y mighty
yulcsuian disturbance, such, indeed, as we
may be certain went on at the early stage Oh
the moons history, TO which these radlating
streaks must be referred. 1t seems Clear tnat'
as Nasmith aas illustrated by experiment,
they belong to that stage OF the moons history
when her still hot and plastic, crust parted
with it's heat more rapidly than the nucleus OF
the rlanet and so, contracting more quickly,
was rent nv tie resistance of the internal
matter, which, still hot and molten, flowed INTO
The rents. and spreading formed the long broad
streaks of brighter surface.
PHOTOGRAPHING THE STARS.
Professor Pickering. of Harvard, described
before the june meeting OF the British Royal
Astronomical Society the method he has been
CARRYING out at Cambridge Observatory OF
photogIaphing the stars, for tne Puip1sse W
determining their color ami relative brightness
We use, he says, a combination Oh lenses,
which gives o comparatively large angular
aperture and a field in which there is not much
tile centre of the field With this combination,
and the sensitive photo graphic plates inat we
employ. stars dowi to the fifth and sixth mag
nitGde leave trace upon the plate no CLOCK
work is employed 30 that each star would trace
a line upon the plate, more or less intense ac-
cording to its brightness Our method Is 10
make au exposure OF ten seconds, 9ut,hg
which tine the earths motion Is so small that
the images of the stars only appear as circular
dots. Then the camera is covered up for ten
seconds, and another exposure OF thfty
seconds is made, so that the image OF each star
is represented by dot and dash. The plates
on which the photographs are taken are about
sir inches by eight inches, and photograph of
a region 150 square occupies about sixth part
Of the plate.
When one photograph has been taken, the
instrument is shifted LOO in declinatlon by
means of spring which fails into notch in
the declination circle this shift can be done
very quickly then another photograph Is
taken tits ti1ne the exposure of thirty seconds
Is made first then there is an interval OF ten
seconds and another exposure Of ten seconds,
so that the image of each star is represented by
a dash and u dot The instrument is again
shifted in decinatioD, and another region OF
I50 is photographed this time the image of
each star is represented by two dashes; then
the instrument is shifted in Right Ascension,
and three more photographs are taken, so that
on one plate of six inches by eight inches we
have the stars IN a region of the heavens meas
urng 500 by 600, that is about twelfth part
of the visible heavens emitting a small region
In the vicinity of the Pole which will have TO be
discussed by another method Twelve such
plates are sufficient to go entirely round the
heavens and complete the work for the north
ein hemisphere.