bulatory and balconies, giving upon
the "Hall of the Universe." This is
reserved for quahfied students only.
Lectures and demonstrations would
be given here, and here would be kept
aU the instruments used in instruction
and the many forms of planetaria,
such as are seen in the German mu-
seums. A hall in the wing is provided
for the lectures and for astronomical
moving pictures. From the balconies
of this hall the student will have an
excellent view of the miniature solar
system.
AEROLITE HALL
First Floor, Street Level
The arrangement of alcoves here
would be somewhat similar to that on
the second floor. The aerolites are
arranged symmetrically in alcoves, the
great aerolites in the largest openings.
This arrangement brings the piers
necessary to support their weight into
positions outside the central hall of the
basement, combining these piers with
the foundation footings of the steel
columns.
SPECTROSCOPIC HALL
First Floor, Continued
This is under Memorial Hall and is
entered from the ambulatory of the
first floor. It adjoins the shaft of the
Hale Heliostat and here beams of
sunHght brought down the shaft can
be utiUzed for spectroscopic projec-
tions.
Vertical shafts are provided for the
Hale HeKostat and the Foucault Pendu-
lum, terminating on the first floor 120
feet below the roof platform. Adequate
elevator service is provided, even to the
observation platform on the roof, where
a telescope and transit will give
opportunity for observation of the
heavens themselves.
The time has certainly come for the
erection of a great educational haU
of the type designed. It is not right
that the United States should longer
remain behind other nations in a field so
important and so absorbingly inter-
esting. The American Museum of
Natural History is, beyond question,
the organization best qualified to
undertake the project. It has an
unsurpassable site, situated at the
heart of the largest city of the Union.
May the means soon be forthcoming
and may the opening of the doors of its
proposed Astronomic Hall soon be
realized.
The Use of Models in an Astronomical Museum
By henry NORRIS RUSSELL, Ph.D.
Professor of Astronomy, Princeton University; Director of Haistead Observatory
THE words "astronomical mu-
seum" might suggest to many
astronomers a collection of an-
cient apparatus which had been rel-
egated to such an environment after
they were no longer of practical use in
the observatory, but there is no reason
whatever why these words should
have such a connotation. While a
museum cannot be so intimately con-
nected with the work of research in
astronomy as it may be in geologj", or
ethnology, it may perform a distinctive
service in connection with its other
great function, that of education, both
of the general public and of more
specialized students of the science.
Direct telescopic observation, which
of course has a unique value, is rarely
practicable for the public, and suffers
under limitations of time even for
university students. These difficulties
maj" be considerably obviated by the
use of photographs, in a manner very
familiar. But it is not generally recog-
nized that suitably prepared models
may perform a mission quite distinct
from that of even the best photographs.
This principle has long been recog-
nized in the field of natural history,
using the word in its narrower sense.
The habitat groups which adorn the
greater museums convey a wealth of
constructive information, even to the
casual onlooker, with which no photo-
graph, however excellent, could possibly
compete. Is it not practicable to do the
same in the case of the heavens?
The more obvious instances, such as
the preparation of globes representing
the moon and perhaps Mars or Jupiter,
have already been frequently at-
tempted. A more ambitious and very
successful attempt is found in the
modern planetarium. But many other
possibilities appear to be open, and it
ma}^ be worth while to speak briefly of a
few, and especially of working models
which exhibit characteristics which
photographs cannot do.
The chief difficulty in explaining
many astronomical problems to the
non-mathematical listener is found in
the fact that the relations which are
concerned are essentiallj' three-dimen-
sional. The power to form a clear
mental image of the relations of several
bodies in space is somewhat unusual,
and pictures in the flat, even the best
perspective drawings, do not altogether
solve the difficulty; while a model in
which the relations are actually repre-
sented in three dimensions will often
make things clearer.
Consider, for example, solar and
lunar eclipses. By a suitable model in
a nearly darkened room, in which all
the light came from a circular opal
glass disk or globe, near one wall, the
umbra and penumbra of the shadows of
the earth and the moon, the track of the
moon's shadow across the rotating
earth, and the phenomena of total,
partial, and annular eclipses, could all
be exhibited. It would be impracticable
to construct such a model exactly to
scale, but the principles involved could
be very clearly illustrated and the
mechanical complications need not be
at all prohibitive.
Again, in the planetary system,
man}^ of the characteristics of plane-
tary motion could probably be best
exhibited with the aid of moving pic-
399
400
NATURAL HISTORY
tures. Were it practicable to prepare a
film after the manner of the "animated
cartoons," which are commercial com-
monplaces, it would be possible to show
the motion of a planet or comet in an
elliptic orbit with velocity varying in
accordance with Kepler's laws. Such a
film, showing for example the motion
of Halley's comet, with some indica-
tion of the change in brightness and the
growth of the tail at perihelion, would
be exceedingly instructive. Similar
diagrams could be used in the case of
binary stars to exhibit both their or-
bital motion around the center of grav-
ity and the rectilinear motion of this
point across the heavens.
But it is among the stars that the
potentialities of the astronomical
models are perhaps the greatest.
Though they seem to us but dimen-
sionless points of light, our knowledge
of the stars is now sufficient to justify
the construction of scale models show-
ing their relative positions in space and
others exhibiting their true dimensions.
The incandescent light here furnishes
us with the great advantage that the
stars can be represented as luminous
points, whose differences both in
brightness and in color can be adjusted
so that they resemble closely those
which actually exist among the stars.
A series of lamps, hung by almost in-
visible wires, could thus form a model
representing the position of the sun
and the nearer stars in space, and
such a model would have the great
advantage that corrections or addi-
tions could readily be made to it as the
discovery of those stars which are our
neighbors in space progresses.
It would be entirely possible, also, to
prepare models in the form of trans-
lucent globes, illuminated by lamps
within, which illustrated both the
relative size and the relative brightness
of such bodies as the sun, Sirius,
Arcturus, Rigel, and Betelgeuse. Most
interesting of all would perhaps be
models of eclipsing variable stars. In
this case two such globes of different
size and brightness would be set up at a
proper distance and caused to rotate
about a common center so that each
eclipsed the other at regular intervals.
There are numerous systems in which
the true dimensions are accurately
known, and with such a model the
visitor might follow for himself the
progress of the changes which, as they
occur in the heavens, would be ex-
hibited by a photograph annexed to
the model.
Still another possibility which occurs
to the writer, is that of a graphical
representation of the relative magni-
tudes of astronomical distances, by
means of a series of models, maps or
diagrams, each on a scale one hundred
times smaller than the last. For
example, one might begin with a
photograph of the room in which the
exhibit is placed on l/lOO or lO-^ of its
actual scale. The next stage might be
an aerial photograph of New York
City, showing the Museum and its
environs, on a scale of l/lO,000 or 10"^.
The next, on the scale of l/l,000,000
or lO"*^, could be represented by a sheet
of the international map of the world.
On this scale the earth is about twenty
feet in diameter, as is illustrated by
segments of a globe, showing the polar
regions, which are now in the Museum.
In the fourth stage, scale 10"^ the
earth would be about 5 inches in diam-
eter, the moon rather more than an
inch, and about thirteen feet from the
earth. In the fifth stage the earth and
moon would be about one and one-half
inches apart and the sun fifty feet
away and not quite six inches in
diameter. The sixth stage would re-
THE USE OF MODELS IN AN ASTRONOMICAL MUSEUM 401
diice the sun to about /{e of an incli,
and put the earth six inches from the
sun. The smaller orbits of the plane-
tary system could be well mapped on
this scale. The seventh stage would
show Neptune's orbit not quite four
inches in diameter, and could exhibit
some of the larger cometary orbits
which are well determined. On the
eighth stage Neptune's orbit would
have shrunk almost to a dot, some of
the cometary orbits would still be
visible and the nearest fixed star would
be some forty feet from the sun. The
ninth stage would bring the nearest
star within a few inches of the sun
and would be well adapted for a model
showing the distribution of the stars in
space. Two more stages would be re-
quired before a model of the Andro-
meda nebula could be shrunk to prac-
ticable dunensions.
The same scheme reversed, so that
objects were magnified instead of
diminished, might perhaps be used to
exhibit the modern discoveries con-
cerning atomic structure. Magnifica-
tions of one hundred- or ton thousand-
fold can be reached with a microscope.
The third stage might be used to illus-
trate the ultra-microscopic particles
which occur in colloidal solutions. The
fourth would exhibit the arrangement
of atoms in crystals, the fifth the
structure of the inner electron orbits in
the heavier atoms; while on the sLxth
the electron itself would begin to be-
come a visible speck.
Such a series of models, if its prepara-
tion should prove practicable, would, in
all probabilit}^, lead to a realization of
the relative magnitudes of the various
bodies with which modern science deals,
and would be much more vivid than
anything that can readily be obtained
at present. The writer will confess
frankly that the realization of this
series is one of his dreams because
he would like very much to see it
himself.
Sectional view of the Zeiss Planetarium
The New Projection Planetarium
By CLYDE FISHER
In charge of Astronomy, American Museum of Natural History
And that inverted Bowl they cill the Sky — ^The Rubaiyat
SOMETHING new has appeared
in the realm of science, something
fundamentally different from all
achievements of the past years in this
particular field. It is an instrument
grand in conception and fully realized
in its development, an instrument for
the purpose of popularizing the great
subject of astronomy.
Our prehistoric ancestors were great-
ly interested in the planets and the stars
and in the sun and moon, and made
considerable strides in comprehending
their movements. The misunderstand-
ings of students before the time of
Copernicus and of nearly all persons for
more than a century after, were quite
natural, for the earth certainly seems
to be in the center of the universe, and
all the heavenly bodies seem to revolve
around the earth. As is well known, the
idea that the earth rotates on its axis
and that the sun is the center of motion
of the earth and other planets was not
accepted without great opposition.
The vicissitudes of this theory, known
as the Corpernican system, the burning
of Bruno at the stake, and the punish-
THE XEW PROJECTION PLANETARIUM
403
meat of Galileo arecominoii knowicdire.
It is true that nieehanisins known as
planetariums showing the relative mo-
tions of the sun, moon, and planets are
not new, but have been constructed at
various times since the days of Huygens
(1629-95) and Roemer (1044-1710).
In England a complicated machine of
this type was built for Charles Boyle,
the fourth Earl of Orrery (1676-1731),
which was named for him, thus
originating the word ''orrerj^" now
frequently applied to such pieces of
apparatus. These machines consisted
of a series of globes to represent the
various bodies of our solar system, each
revoMng globe supported by a metal
rod, the W' hole system of sun and planets
and satellites being connected and
propelled by gears so that their relative
motions were approximated. The
earlier ones had much to do with the
final general acceptance of the Coper-
nican system and, ever since their first
appearance, these devices have had
and still have great value in teaching,
the three-dimensional mechanisms cap-
able of suBulating the motions of the
heavenly bodies being incomparabl}'
more effective than flat pictures or
pages of printed text.
Some of these mechanical plane-
tarimiis or orreries have been made
with great ingenuity and skillful work-
manship. The best ever constructed
was made by the Carl Zeiss Optical
Works and is installed in the German
Museum in ]\Iunich. It may be briefl}^
described as follows: A lighted globe
in the center represents the sun. The
sLx planets nearest the sun, wdth their
satellites — the planets and satellites all
revolving at their proper relative speeds
— are shown. The diameter of Saturn's
orbit is about forty feet. Uranus and
Xeptune are left out, I presmiie be-
cause their tremendous distances would
make the rest so small proportionately.
There is no light except from the central
sun, and the walls, ceiling, and floor are
painted black. Consequently, day and
night are well shown on any of the six
planets, and so are the phases of our
moon. For the lecturer or demon-
strator, a car travels around under the
earth, which goes around the sun in
twelve minutes, the apparatus being
propelled by an electric motor. The
phases of Venus and Mercury can easily
be observed. The constellations of the
zodiac are shown in a belt on the wall,
with their names in white letters and
with the degrees of the ^circle marked.
The principal stars are shown by lights
back of small, round holes in the black
wall.
Yet, in view of all this, it is quite
plain that these old-fashioned plane-
tariums or orreries w^ere veiy crude
WfS^WBT^:.
ZEISS
Planetarium
Aorluhrungen:
soonlags II .'â– '^ A''
This way to the Projection Planetarium,
at the Zeiss Optical Works, Jena
and unsatisfactory at best. All were
built on a smaU scale and the observer
had to watch the various movements of
the heavenly bodies from the outside
of the solar svstem. and not as one
404
NATURAL HISTORY
observing from the earth. And in all
cases the comparative sizes and dis-
tances were more or less extremely
distorted. And again, the fixed stars,
which so enthrall us in the night sky,
were always left out, although some-
times shown in an inadequate manner
by being painted on the surface of an
outside sphere or zodiacal zone or belt.
It is true that some of these defects
were partially overcome in the large
Copernican planetarium in Munich,
described above, but all of the old type
are conspicuously inadequate in com-
parison with the new projection plane-
tarium.
One of our American astronomers,
in a recent number of a magazine de-
voted to astronomy, says "it has been
reserved for Dr. Bauersfeld of the Carl
Zeiss Optical Works in Jena to make
the first complete solution of this
problem, so significant in the ultimate
Zeiss Projection Planetarium on the roof of the Carl Zeiss Optical
popularizing of the noblest of the
sciences, thus enabling for the first time
in history the 'man on the street' to
comprehend quite as fully as the learned
professor, the seemingly intricate,
though actually simple workings of the
celestial mechanism."
Before the outbreak of the World
War, Dr. Oskar von Miller, director of
the German National Museum at
Munich, approached the Zeiss firm
regarding the construction of a plane-
tarium which would show the move-
ment of the heavenly bodies according
to the Ptolemaic system on the interior
of a hemispherical dome in the same
manner as they appear in the heavens
to an observer on the earth, that is, to
one inside the universe. The first idea
considered was to represent the stars
by small electric bulbs attached to the
dome which would have to be rotated
around an axis parallel to the earth's
THE NEW PROJECTION PLANETARIUM
405
Works, Jena, Germany. Crowds arriving to witness a demonstrati
axis. The sun, moon, and planets were
to be represented by illuminated discs
driven by suitable gearing in such a way
that the epicycle orbits of the heavenly
bodies would be truly represented. It
soon became evident, says Dr. Ing. W.
Bauersfeld, that it was impossible to
solve the problem in this manner, and
the outbreak of the war put a stop to
the work. It was taken up again after
its close, but the problem was attacked
from an entirely different point of
view.
The basic idea of the solution was to
have the hemispherical dome fixed and
to throw images of the heavenly bodies
on the dome by means of a projection
apparatus located at the center of the
dome, the apparent movements of the
sun, moon, planets, and stars to be
accomplished b}^ the mechanism of the
projection apparatus.
In 1924 the first projection plane-
tarium was completed and installed in
the Munich Museum. In September,
1925, it was my good fortune to be sent
to Germany b}^ the President and Board
of Trustees of the American Museum of
Natural History, for the purpose of
examining this apparatus with a view
to its suitability for our proposed Hall
of Astronomy. There is no museum of
astronomy or department of astronomy
in the world that compares with that
in the German National Museum at
Munich, and the most impressive and
consequently the most popular piece of
apparatus in the whole astronomical
department was the new Projection
Planetarium. The available space
allowed only ten meters for the inside
diameter of the dome. The INIuseum
had two lecturers, who together gave
nine demonstrations a day. I attended
one of these, at which a part of the
audience was made up of a large class
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THE NEW PROJECTION PLANETARIUM
409
of pupils from a parochial school ac-
companied by two or three nuns.
The second Projection Planetarium
to be built was located upon the roof
of the buildings of the Carl Zeiss Works
at Jena, and it was here, before going
to Munich, that I first saw the
apparatus in operation, and it was here
that I made a careful study of the
mechanism and its working. The dome
is larger than the one at Munich, being
sixteen meters or about fifty feet in
diameter, and affords seating room for
280 persons, although in the excite-
ment of the first days as many as 600
persons, more than half of them stand-
ing, were packed into this dome, and as
many as twelve lectures and demon-
strations a day were given. The dome
is hemispherical in shape and is white
inside. In the center is an optical pro-
jection apparatus which throws on the
inside of the dome images of the sun,
moon, all the planets which are visible
to the naked eye, and the 4500 fixed
stars that are visible to the naked eye,
including the Milky Way. These pro-
jected images move as the real bodies
appear to move in the sky, with the time
accelerated due to rotation of parts of
the central apparatus, which is so
accurately made that it takes care of
the precession of the equinoxes. The
erratic motions of the planets in the
sky as seen by the naked eye from the
earth are visualized much more satis-
factorily than by the old-fashioned
planetarium.
The phases of the moon are just as
clearly shown, but most impressive of
all is the realistic appearance of the
fixed stars, including the Milky Way.
In the public demonstrations at Jena
the audience was sometimes composed
largely of school children. Whether
the audience was made up of children
or of adults, when the fixed stars
appeared, an involuntary "Ah" swept
over the assembly and they were spell-
bound. It seems that no one is pre-
pared for such a realistic repi-esenta-
tion, and I was no l^ettcr prepared than
others. In short, I was astonished,
overwhelmed. The illusion of the
immensity of space is perfect. One
feels that he is in the great outdoors
under a clear night sky. Due to some
subconscious imagination, perhaps — at
least for some psychological or physio-
logical reason, this artificial sky seems
to possess the deep night blue seen in
the real sky, and yet there was no blue
color on the inside of the dome and
none in the projection apparatus. On
being congratulated upon the mechan-
ism, Dr. Ing. W. Bauersfeld, the inven-
tor, admitted that the illusion of the
immensity of space and the realistic
representation of the fixed stars, in-
cluding the Milky Way, had exceeded
even his expectations. And Dr. W.
Villiger, head of the department of
astronomy in the Zeiss Works, was an
unbeliever until the apparatus was
finished and demonstrated.
By means of a special set of projec-
tors the names of the constellations can
be shown in the sky, and with a flash-
light showing an arrow-shaped light the
lecturer can point out any star, planet,
or other body in the sky.
During several days spent at the Carl
Zeiss Works I was afforded every facility
for examining this new invention, in-
cluding several private demonstrations,
besides the opportunity of attending a
number of public demonstrations. For
the latter they have five lecturers,
young men with technical training who
during part of their time are otherwise
engaged in the Zeiss Works. Full notes
were made concerning the apparatus,
its installation, its demonstration, and
its adaptation to our astronomical
410
NATURAL HISTORY
Spraying liquid concrete on skeleton of dome of Zeiss Planetarium
hall at the American Museum.
In early September eleven of these
planetariums had been sold to cities in
Germany, and negotiations were in
progress with other cities of Europe.
Within a few days they expected to
close a contract with Vienna. One of
the domes in the process of building
was seen and photographed in Prinzes-
sinen Park in Jena. In this the dome is
twenty-five meters, or a little more than
seventy-five feet in diameter, almost
exactly the same diameter as the dome
planned for our astronomical hall. In
the one at Diisseldorf the dome will be
thirty meters or more than ninety feet