The morning call., 1893-10-16
THE FIXED STARS.
Their Actual Dimensions
May Be Known.
What Professor Campbell Has Ac-
complished at the Lick
Observatory.
Correspondence of THE MORNING CALL

To the Editor Of the CalI-SIR: l desire
portant discovery which has lately been
made at the Lick Observatory by Professor
Campbell. His paper containing the
technical details has just been sent to the
scientific journals, and it is proper time
to give more popular account.
Our knowledge regarding the stars has
long needed the addition of one fact One
question has hitherto remained unan-
swered. namely: What are the actual di-
men sions of the stars, or of any one star?
The distances of a number of stars are
quite accurately known. considering the
difficulties OF the determination. The
masses of few stars are known. and
these masses are not very different from
the suns mass. They are at least of the
same general order OF magnitude. The
chemical constitution of many of the stars
is we'll known from spectroscopic observa-
ton. The motions OF many stars in the
line of sight-joining the earth and the
star-are also well known from similar
observations. and their motions in direc-
tions at right angles TO the line OF sight
are known from observations made with
meridian Instruments.
w ucD W0 tn0 cuUl ulS-
tances of stars in general and the COM
paratively small amount of light of each
star, it must be admitted that much has al
ready been learned regarding them. One
datum is still lacking What are their actual
dim IN sions or what is the actual diameter
of any one star2 This question has been
hitherto unanswered, and 1t ls a capital
one. AS the stars in general are of the
same order of mass as the sun. it is to be
presumed that they are also Of the same
order of size. But 1t is aqueston needing
solution.
very ingenious method for doing this
has been invented, and it will probably be
tried at Mount Hamilton. 1t IS so delicate,
however, and beset with so many practical
difficulties that while the principle of the
method is entirely correct, success in its
practical application is very doubtful.
The question has. however, been solved
by Professor Campbell for one star in an
unexpected way in the course of his
spectroscopic observations. The principle
employed by him has previously been ap-
piled with reference 10 the sun in the same
manner. The solar atmosphere contains
many different substances so highly heated
as to give out light. These substances are
arranged in the suns atmosphere in the
order of their densities. the heavier ones
lower and the lighter ones higher. The
length of The spectral lines of each SUBJ
stance tells the height to which it extends.
This observation Is not very difficult in the
solar spectrum. but it was entirely unex-
pected when Professor Campbell found a
star Cd. Nj. 80 deg. 3639) with bright line
spectrum surrounded by an atmosphere of
hydrogen gas of such enormous extent as
to be measurable.
This hydrogen sphere surrounding the
solid nucleus of the star is five seconds of
arc In angular diameter. When the dis
tance of the star is known land ob serya-
tions to this end are in progress) til is ang-
ular diameter can be expressed in miles.
Then for the first time we shall know the
actual dimensions Of one Of the .fred stars
This discovery of Professor Campbeis is
absolutely unique. and it opens an entirely
new field of knowledge. 1t is so important
that il should be known at once. Very
respectfully, EDWARD S. HOLDEN.
Lick Observatory. Oct. 13. 1898.