Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1899-02-15

turtles the one universal astfonofrmcai
text book.
A modern catalogue contains, hke
that of Ptolerny, four columns OF entry
The first gives the stars designation
the second am indication or us DfiSat-
ness; the third and fourth the ds-
examinations OF ITS place. 1lhese are
EXPRESSED In two directions, whtch, ~
modern catalogues, not in Ptolemy D.
correspond ON the celestial sphere 70
longitude and latitude ON the terreS-
trial Distance north or south OF the
celestial equator Is termed "dechna-
tIon,' corresponding to terrestrial lati-
tude. Distance lin a direction parailei
20 the equator is termed right asceh-
SION" corresponding to terrestrial
longitude For geographical purposes
we conceive the earth to be encif'cled
by two imaginary lines at right angles
to each other-the one, the equator.
marked out for us by the earth Itself;
HE other. longitude nought," the
meridian of Greenwich. fixed for us by
general consent. after the lapse OF cen
turtles. by kind of historical evolution.
On the celestial globe in Ike manner
we have two Fundamental hnes-one,
the celestial equator, marked out for
us by nature; the other at right angles
10 IL, and passing through the poles OF
the sky. adopted as "A matter Of con-
ven,ence But difficulty al once con-
fronts us--w here can We fix our right
ascension nought? What star has the
right to be considered the Greenwich
of the sky?
The Difficulty Is met in the following
manner: For six months Of the year,
the summer months. the sun is north
of the celestial equator; for the other
SIX months of the year the months of
winter il is south of 1t. 1t crosses the
equator, therefore. twice IN the year
once When moving northw ard at the
spring eqlAnox: once when moving
southwark al the equinox of autumn.
The point where IL crosses the equator
at thu first of these times il taken ~
the Fundamental point of the heavens.
ard the first sign Of thu zodiac. Aries
the Ram il said To begin here, and il IS
called. therefore. the first point Of
Aries
One Of the very first facts noticed Il.
the very early days Of astronomy was
| hat as the stars seemed To move
| across the sky night by night, they
seemed 10 move In uns4 solid piece as If
| they We're lamps rigid.y fixed in one
and the same Solid vault, OF course. Il
has long been perfectly understood
that this apparent movement was not
N the least due To dny motion Of the
stars. but sfmply Ia the rotation OF the
earth On lis axis This rotation Is the
smonthest. mast constant. ami regular
movement of which Ne know. IL fol-
lows, therefore that the interval ID
time between The passage II one star
across the mprlti.a:g of Greenwich ana
that Of any other given star is always
tAe same This interval of time Is
simply the difference If their right as
cension. If we are able. then. 10 turn
our transit instrument to the sun. and
to a number of stars, each in its proper
turn ana by pressing the tapping
p.ece on the instrument as the sun u
star comes up TO each of the Ten Mires
IN succession. 10 record the times OF its
transit ON the chronograph, we shall
have practically determined their right
ascensions--one IF the two clements II
their places.
The other element, that of declina-
ti9n, is foumi in a different manner
The celestial equator, like the terres-
trial is 90 degrees from the Pole. The
bright star Puaaris is not exactly at the
Nortin Pole, but DESERVES a small
circle round ii. Twice in the II hours
ii transits over the meridlan-once
when going from east 10 west it passes
above the Pole, ONCE when ss5iIg from
west to east below the Pole. The mean
between these two attitudes Of Polaris
above the horizon gives the position of
the true Pole.
a complete transit observation of a
star consists Therefore oil two operations.
me observer sees a star entering the
held OF the telescope: and as it swims
forward he presses the galvanic button
which sends II signal to the chronograph
as the star comes up to each of the ten
vertical wires in succession. But beside
me ten wires there are others. Two YER
Iical wires lie outside the ten. and there
Is also a horizontal wire. The latter can
pc moved by a graduated screw head
Just above the eye-piece. and as the star
comes III succession 10 these two vertical
wires, this horizontal wire is moved by
the screw head. so as to meet the star
at the moment it is crossing the vertical
wire, and the observer presses a second
OF the horizontal wire on a small paper
covered drum, Then. the transit over,
the observer leaves the telescope and
comes round to the outside of the west
pier. Here he finds seven large micro
scopes which pierce the whole thickness
OF the pier and are directed towards the
rigidly attached to the telescope and re-
wolves with it. This wheel is six feet in
diameter, and has a silver circle upon
both faces Each circle is divided care
fully into 1920 divisions-these divisions |
therefore. being about the one-twentieth |
of an inch apart The lowest microscope
is the least powerful. and shows Il large
part of the circle. and enables the OBJ !
server to see at once TO what degree ana |
division of a degree the microscope is |
pointing. The other six microscopes are |
very carefully placed so degrees apart |
Fhtse microscopes are all fitted with !
movable wires-wires moved by Il very |
me and delicate screw. the screw-h head |
| having divisions upon ii that the eX- |
act amount of its movements can be told !
Each of the six serewheads will read to !
the hve-t housandths part of division OF |
the circle. in other words. To the one |
hundred thousandth part of an inch. Us |;
ing all six microscopes. and taking their !
mean. we are able to read to the one !
hundredth of IL second of are. IT, there |
fore. the observations could be made |
with perfect certainty down to the ex- |
tremist nicely of reading which the in |
strument supnnes, we should be able 10 |
read the declination of a star to this de- |
gree of refinement
The process of reading the stars is ex- |
citing ard interesting. The observer sets |