The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1901-05-05

Ials, q certain prescribed irregularity re
suits IN the marks on the chronograph
sheet, so that when the record is read
1t becomes easy to determine which is
tho Y made by the observer and which
by the pendulum At night the cross
hairs are Illuminated by a little lamp
at the side, and shine golden against
the deep blue of the sky and the silver
dots of the stars.
Taking the time star" is one of the
most delicate of observations; the in
strument must be adjusted to catch the
star at the very point where it crosses
the meridian. Certain stars, the positions
Of which have been definitely determined,
are Used as o'clock stars all observa-
of stars in the celestial equator. Tho
reason for this is that while every star
takes the same tine-a sidereal day-to
make its apparent passage around the
the pole star, for instance, followinS a
circle hardly noticeable. SO that its move
ment is hard to detect with the naked
eye. A star further toward the celestial
equator is on o larger circle, and one
On the equator on a yet larger or greater
circle. seeming to travel past the vertl-
cal threads at express speed 1t is to
secure standard records that observa-
tiOEs of the o'clock stars" are all 5ubse-
uuently calculated on the common equa-
torial basis. The work involved in this
seemingly simple observation gives an
outsider an idea what modern astronomy
calls for in the observers and comput-
ers.
Strange as 1T seems, observations for
sidereaI time are often taken in bright
daylight, the meridian circle in use at
Cambridge being able, if the weather is
clear, to detect stars Of the first. sec
ond and third, and occasionally Of the
such brilliant stars as Sirius and Capelia
may be used, the passage of which over
the cross hairs can be more accurately
determined. Speaking Of time observa-
lions. those made with the meridian cir
Gle at Cambridge, of Nova Persei, the
new star recently discovered by DR.. T.
D. Anderson, of Edinburgh, which sud
denly famed up and then died down,
were all made by daylight; the photo
graphic plates from which its history was
determined when it's discovery was an
nounced, were. Of necessity, however,
taken at night.
tricity is widely used in Cambridge, for
Prof Edward G. Pickering the director.
and Mr.. Willard P. Gerrfsh have made
a special study of the matter. In one
of the many buildings on the hill are
the electrical headquarters. In the base
ment is a storage battery of thirty cells
from which power is constantly deriTs>.
Along the wall are several large pendu-
lum clocks with no dial the works show
ing somewhat pathetically behind the
glass fronts where the dials ought to be.
On the rod Of each pendulum IS little
shelf on which are placed small brass
scale weights. an ingenious device Of as
tronomers to raise or lower the center Of
gravity of the pendulum-or il other
words to shorten or lengthen It, making
1t beat faster Or sloWer-W1tho'tt disturb
ing it or the works, as might be the case
if the Dob were moved up aud down
by the screw nut below it. A clock is fist
approximately regulated by the nut and
then exactly re gulated by the weights to
suit whatever Instrument it is used TO
control
On the bottom of each pendulum rod Is
fastened little device which originated
at Cambridge, and which is designed to
avoid the friction In tho case. of the ordi-
nary pendulum, which makes and breaks
a circuit by direct contact This device
liz nothing more or less than q chlld's-
horseshoe or permanent magnet, with its
familiar red paint and all. Below 1t Is
fixed armature of soft iron on the end of
a spring and as the magnet gees back
and TO, tn in passing. 1t attracts the arna-
ture which Ia rising is arrested in little