The times. [volume] (Washington [D.C.]) 1897-1901, 1901-01-13

Inc nrSt extensive catalogue or stellar
spectra was published by Vogel. 1t dealt
with 405l stars and appeared in 1883: 1t
has since been followed by the Draper
catalogue based upon photographs of the
spectra which contains much larger
number. With regard to aebulae Herschel
published his third catalogue in 1902 The
last catalogue of this nature Is by Dreyer
dsss) and contains I. so of these objects.
In the time of Tycho they could be count
ed on the fingers of one hand.
INVESTIGATIONS OF SOME IMPORTANT AS
ECONOMICAL CONSTANTS.
The century has been fruitful in the de-
termination Of many numerical values
which are all important In enabling us to
determine the distance and masses of the
heavenly bodies. thereby giving us firm
grasp not only of the dimensions of our
own system, but Of those scattered in the
celestial spaces.
To take distances first. We must be-
gin with the exact measure of the earth;
for this we must measure the exact length
of an are of meridian or of parallel, that
is, a stretch of the earth's surface lying
north and south or east and west. between
places of which the ATTITUDES are accurate
ly known in the former case and the
longitudes in the latter. In either case we
can determine the number Of miles which
go to a degree. Beginning at the opening
of the century with an arc of meridian of
2 degrees measured by Gauss from Coffin
gen to Altoona, the arcs of meridian have
grown longer as the century has grown
OF an arc of meridian from the Cape to
Cairo. embracing something Ike IS de-
grees of latitude, is being mooted.
The measurements OF arcs of parallel
have been developed by the rapid extern
sion of Geographic communications which
now permit the longitude of the terminal
stations to be determined with the great
est accuracy.
Thanks to this work, we now have the
polar diameter is a. 100. 80 feet, but the
equator is not a circle. the equatorial
diameter from longitude degrees Is min
utes west to longitude 1ss degrees Is min
utes west \ 1.s53.25S feet; that at right
angles to it is f1,s50210 feet, that is, some
thousand yards shorter. The earth. then.
IS shaped Ike an orange slightly squeezed.
Knowing the earths diameter, we can
obtain the suns distance by several meth
DDS, the old one by observing transits of
Venus, e of which Cooke went out to
observe in 1863 and two of which required
in 1874 and 1882; new ones by observations
of Mars. or one of the minor planets at
a favorable opposition. and by determin-
ing the velocity of light.
The recent discovery of a minor planet,
Eros" which in one part of its orbit is
nearer the earth than Mars, has recently
revived interest in this method, and
combined attack is in contemplation.
1t has long been known that light has
finite velocity, but we had to wait till the
'6es before Fizeau and Foucault showed
us how to determine its exact value. The
methods introduced by them have been re-
Gently applied by Cornu, Newcomb, and
Nicholson. and the resulting value is
slightly less than 100000 metres per see
ond. Combining this with the constant Of
alteration. the distance of the sun can be
determined
1t is wonderful how these vastly differ
emf methods agree in the resulting mean
distance. At the beginning of the century
il stood roughly at IS, Oo0,G50 miles; this has
been reduced to s3,965.o00 miles. The ex-
IRENE difference between the old and the
new values of the solar parallax, two
fifths of second of arc, is represented by
the apparent breadth of a human hair
viewed at distance Of about 125 feet.
Knowing the distance of the sun, the
way is open to US to determine, by a
method suggested by Calico. the dis
tances OF those stars which occupy diff
ferent position among their fellows as
seen from opposite points in the earth's
orbit round the sun, points 1850 go miles
apart. We now know the distances of
many such stars. Bessel having deter
mined the first in 1885 The nearest star
to us. so far as we know. is Centauri, the
light Of which takes four and a half years
to reach us. Not many years ago Pritch-
ard applied photography to this branch OF
enquiry: we may therefore expect a still
more rapid progress in the future.
With regard to masses. We naturally
must first know that of the earth; having
its size. If We can determine it's density,
the rest follows.
The problem Of determining the mean
density of the earth has occupied the
minds of many workers during the clos
ing century. Newton about 1879 pointed
out how it could be deduced by observing
the deviation from the vertical of plumb
Tne suspended near a large mass of mat
ter-a mountain the volume and density Of
which could be previously determined
This method, which is very iaborious and
requires the greatest skill and most deli
cate Instruments, has been employed sew
eral times, by Bouguer and Condamine In
1873 at Chimborazo, Maskelyne in 1774 at
Schehallien in Scotland. and James at Ar
thurs Seat, near Edinburgh.
At the beginning of the century another
method was introduced by Cavendish.
This consists in measuring the attrac-
ton of two large spheres of known size
and mass, such as two balls of lead, on
two very small and light spheres. by
means CT torsion balance constructed by
Mitchell for this purpose.
The most recent determination by this
method, and one which is considered to
give us perhaps the most accurate value,
Is that which is due 10 the skill and in
genuity of Prof. Boys. His Improvement
consisted in constructing most delicate
torsion balance: the attracted spheres con-
sisted OF small gold balls suspended by a
quartz fibre carrying a mirror to indi-
cate the amount of twist. The whole in
strument was quite small and could easily
be protected from air currents and
changes of temperature, while the use of
the quartz fibres reduced to n minimum
one of the greatest difficulties of the Cav