The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1897-05-23

| ulreCI or OtuerWlSe, Out tueIo az uoW al
impression that the solar type as whole
are nearest to the sun, as if the solar
stage of development found correspond
ing allotment in the starry realm. But
neither the discovery of stellar constitu-
ents, nor the goal of the sun, is the aim
OF the spectrographic work in progress at
Mount Hamilton; though there is no
doubt but that it will eventually benefit
both branches of research, which are akin
| to it in different ways.
| Professor Campbell engages in his
| arduous task unhampered by preconceived
ideas as to star drift. and in a certain
sense. holding his mind aloof from all
| lnferences derived from previous inves-
| legations, spectroscopic or otherwise as to
stellar motion, turns the grand equipment
at his command to the sole aim of accu-
| mulatlng the best prncurable data. That
this expectation is fully warranted, there
Is no doubt as the most eminent explorers
In the past have not been equally equipped
for this work. Vogel, though using q
! spectrograph since 1883. until quite
recently, had but medium sized tele-
scope; and the excellent equipment of
Professor Pickering for spectra photo
graphy, as it includes a slitless spectre
scope, is untitled for observations in the
line of sight. The contradictory evidence
OF observers as to the rate of recession of
Arcturus, which is one of the orbs at
present under photographic scrutiny at
the LICK Observatory, shows the extreme
| difficulty OF such estimates.
Formerly the supposed rate was fifty-
five miles per second, but this is now cor.
rected by the concurrent measures of
VogeI, Keller and Campbell to four miles
per second. An idea may be gained of
| the spaces to be measured by glancing at
the space between the two close lines un-
der the letter D in the representation of
the suns spectrum. If line were dis
| placed one-fortieth of that space it would
indicate journey in the line of sight of
about four miles per second.
1t is customary to express the wave
lengths OF light in tenth meters, and as
they range from less than 1000 in the vic.
let to nearly 5000 in the red, the wave
length of line explains Its position in
the spectrum.
Professor CampbelPs observations will
be chiefly confined 10 those lines between
1850 and 1920, which correspond with those
under G in the illustration. Many of these
are well.known hydrogen lines, but he
also expects to use calcium and iron lines.
This is the violet end of the spectrum to
which the Photographic plate is most sem
sitive. Sirius yields the i'm press of it's
spectrum in twenty seconds, whereas Arc
turus requires three minutes. chiefly ow-
ing to the scarcity of actinic rays in its
spectrum. At present solar stars are
being observed and later on attention will
be given to Sirian and red stars, accord
ing as favorable specimens of each class
come to view. AS three nights per week
will be devoted to this work during the
coming five years it is expected that about
600 stars Will be used, including orbs from
first to fifth magnitude OF the Si-ian and
solar types, and from first to third or
fourth magnitude of the red types, thus
accommodating large amount of data of
the mig hest order OF accuracy.
The G rossley reflector, already renowned
for its Photographic work. will take the
place OF refracting light gatherer for the
spectrographic prisms ct times and also
the Pinch refractor according to the re-
quirements of the object viewed and at.
mospheric conditions. That the scope of
these researches will lead to grand and
reliable results can scarcely be doubted,
but they may be partly negative. They
may be confirm atory of the meager evil
dence before CLEANED, or they may re.
flute previous testimony as to motion in
the line of sight aud perhaps too as to
the apex OF the suns wav. There may be
some drawbacks as yet unknown to the
value OF the data, as is suggested by W.