The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1895-12-25
PHOTOGRAPHS OF THE sUN.-Pho-

useful handmade to astronomy in many
fields, and in no one more than in record
ing the features of the suns surface and
surroundings. One of the first instruments
purchased for the Lick Observatory was
the horizontal hoto-heliograph, which
was invented for the purpose of making
photographs of the solar surface. Sys-
tematic observations of this kind have
been carried on at Mount Hamilton
since August, 1893, by Mr.. Per-
rine, and our collection of sun-nega-
tives already numbers 1900 plates.
The image of the sun on these plates Is
about four inches in diameter and the
picture is on scale large enough to show
not only the spots themselves, but the de-
tails of their structure. Whenever the
conditions of vision are favorable these de-
tails and the forms OF the facule are beau
tifully distinct and such pictures readily
permit of an enlargement of three diam
eters.
Like all astronomical photographs, such
plates give the data required for study, but
valuable results are only to be reached
after such a study has been made. Each
of our plates should be measured so as to
give the area of the spotted portion of the
suns disk in fractions of the whole disk,
and this because the relative amount of
spotted surface is a measure of tho suns
activity. The latitude and longitude of
each spot should also be determined, so as
to deduce the laws of the suns rotation,
etc. The sun. being fluid body, does not
rotate according to the laws which govern
the motion of rigid body, like the earth,
| for example. To make the measures which
have lust been spoken of would require the
whole time of one observer, and it has not
yet been possible to spare the time from
! other and more important duties. Our
collection OF negatives remains, therefore,
as very complete history of the solar
changes during long period, but will not
! show it's full value until the services of an
other observer are available. At Green
wich five persons are employed in this
work alone.
In order to study the finest details of
solar structure it is desirable to have the
photographs on as large scale as pos
sible. For this purpose a special piece of
| apparatus has been made (and presented
to the observatory by DR.. A. Blair Thaw
| of Santa Barbara), to be used with the
great telescope. 1t is expected that the
large-scaIe photographs obtained in this
way will enable the structure of the spots
to be studied to great advantage.
| Photographs OF the Moon.
| The great telescope is regularly en-
ployed in making photographs of the
moon and planets for the purpose of re-
cording the lunar features as they change
! in appearance from hour to hour and
| 10 ~ %
satellite. The lunar photographs are
taken in the focus of the great telescope
| (the image of the whole moon being about
five inches in diameter) and also enlarged
directly five times. The negatives thus
obtained are subsequently enlarged to q
| standard size for the map of six feet to the
| moons diameter.
| Some special regions are enlarged to q
| scale of twenty feet to the diameter.
| Considerable improvements have been
made in this work during the past year,
especially in the Photographic processes,
and the resulting pictures are entirely
satisfactory. The material for making the
moon map is now in hand, but there are
| 10 funds available for the publication of
such map.
Under these circumstances duplicate
| negatives have been sent to other observa-
tories in the United States and in Europe
so as to make our work Immediately use
full, and it is possible that the funds to
publish the moon map may be provided
| by foreigners. This is not as it should be-,
| but there appears to be no help for it,
unless some generous American friend will
provide the necessary funds. The uni
versity can spare no money for the ex-
pensive heliogravure plates which are re-
CURED.
No matter how the moon map is
eventually published full credit will come
to the Lick Observatory, because the map
must be based on our negatives.
The new Crossley reflector will be
splendid addition to our Photographic
equipment, since it is especially suited to
the photography of nebul@ and comets.
A Photographic refractor of five inches in
aperture, formerly the property of Captain
r. s. Floyd, president of the Lick trustees,
has been presented to the observatory by
his daughter, Miss Floyd of Lakeport.
This instrument is exactly suited for
eclipse expeditions, and will probably be
used by Lick Observatory party at the
total solar eclipse of August, 1896, in
Japan. The funds to send such an ex-
petition will probably be provided by
generous friend of the observatory.
During the year Professor Barnard COM
pleted his series of negatives of the Milky
Way etc., and is now preparing them for
publication. They will be issued as
quarto volume by the Lick Observatory,
the necessary funds to print the plates
having been subscribed by private persons.
All the spectroscopic work Of the observ-
atory is done by Professor Campbell, using
a splendid spectroscope presented to US
by D. o. Mills. The observations relate
to the motion of the stars in the line of
sight, to the spectra of planets, stars,
nebula, comets, the aurora, and have inn
portant bearings on such questions as the
constitution of Saturns ring, of the atmos-
pheres of the planets, of the motion of the
solar system in space, etc. This is not the
place to present the results of such work.
1t may be added that the new Crossley
reflector will be powerful aid in the
spectroscopic problems.
Meteorological observations are regularly
made at Mount Hamilton thrice daily.
Eartbouoka nhenomena are reoord ed outo-