Geodesic Domes and Charts of the Heavens
The world's first lightweight steel structural framework was built on the roof of the Carl Zeiss optical works in Jena, Germany in 1922. When covered with ferro cement the structure became the first thin- shell concrete structure in history. What is even more remarkable about the dome is that it was almost incidental to a spectacular scientific and technical accomplishment: invention of the planetarium projector. The inventor of the projector and the dome was Dr. Walter Bauersfeld, chief designer at the Zeiss works. A brief history of the astronomical devices that led to these inventions follows; it is a story of the foremost breakthrough in astronomers' attempts to "create the illusion of the mysterious, silent march of the worlds of nature."
Although the concept of the sky as a sphere may have occurred as early as 2,000 BC in China, it is recorded that in the 6th century BC. the Greek Anaximander taught that the stars and planets pass not only above, but beneath the earth. Greece's first scientific astronomer, Eudoxus of Cnidos (about 400 - 355 BC) constructed the first known complete celestial globe, which became the model for future globes. In 73 BC, in Italy, a white marble statue was discovered, depicting the god Atlas supporting a celestial sphere which is 26" in diameter. On the sphere are inscribed not only constellations, but circles representing the elliptic boundaries of the zodiac, and the major parallel circles.
Many globes and charts of the heavens appeared after (and before) the Farnese Globe; but the first real instruments of astronomy were the armillary spheres, which consisted of a framework of circular rings representing the various astronomical circles, and horizontal rings to indicate the horizon, equator, elliptic (path of the sun) and a vertical ring for the meridian. One such device, the Gottorp Armillary Sphere, built in 1653 by Andreas Busch was a marvel of craftsmanship and art, mechanized to show movement of the sun and with six silver angels representing the known planets. The part of the framework bearing the equator was made to rotate with respect to the zodiac at a rate corresponding to one revolution in 25,000 years, which is the rate of the processional motion of the earth.
A remarkable device, also constructed by Busch in Germany in 1664, was the Gottorp Globe, a water- powered 3 1/2 ton, 10 foot diameter sphere that rotated once every 24 hours. Inside it was a platform for 12 persons and on its interior was a map of the sky with gilded stars. All other globes to that time had shown the sky from the unnatural position of the observer on the outside of the celestial sphere.
Early in the 18th century, a fine mechanical planetarium was built by John Rowley for Charles Boyle, fourth earl of Orrery. Called the "Orrery", similar instruments since have borne the same name. These devices incorporated the "new" concept of the solar system originally proposed by Copernicus, that the earth was round and revolved around the sun once a year.
In 1758 a large globe was built by Roger Long at Cambridge. It was 18 feet in diameter and accommodated 30 people. In 1913 Dr. Wallace Atwood, director of the Chicago Academy of Science designed and built a 15 foot diameter electrically driven globe that is still in use today.
The difficulty faced by astronomers at this point in history was constructing a globe to accommodate a much larger audience. In 1913 the Carl Zeiss optical works of Germany understood the problem of designing a huge sphere that would both hold a large number of people and show the motions of the planets as well as the stars. After much work, no satisfactory solution was found. Then in 1919, just after the end of World War I, Dr. Walter Bauersfeld of Zeiss:
...caught an entirely different idea: reversing the plan of a mechanically rotatable hollow sphere with illuminated images of the stars, he transferred the entire mechanism for the movements to a collection of projectors which would project luminous images of the stars on to a stationary white hemispherical dome of much larger dimensions than those originally conceived. Within the dome, the centre of which would be occupied by the projectors, all would be in darkness. By means of suitable mechanisms the projectors would be moved and guided so that their illuminated images of the heavenly bodies would conform on the dome to the motions which actually occur in nature...
For five years a large staff of scientists, engineers and mechanics worked with Bauersfeld at the huge Zeiss plant in Jena, Germany to design the projector and the projection dome.
The projection of the starry sky required a certain number of projectors, arranged in the center of the dome. Each projector should illuminate an area of the same size as the dome. If the vertices of an icosahedron are cut in such a way that the new surface consists of 12 pentagons and 20 hexagons the area within each is nearly of the same size. The projectors are arranged in the centers of the pentagons and hexagons and produce 32 starfields on the same dome. (Actually only 31, since one area is used for the support.)...
To test the projector Bauersfeld needed a hemispheric dome as a replica of the sky. It had to be lightweight, as it was to be placed on the roof of the Zeiss factory in Jena. He built a light iron rod framework, the design a highly sub-divided icosahedron, with great circle arcs. Thus both the dome frame and the projection pattern were derived from the icosahedron.
Not until the complex skeleton (3,480 struts accurate in length to 2/1,000 of an inch) was complete did Bauersfeld seek professional construction advice.
We planned to cover it first with a fine network of thin wire in order to embed the whole construction in a layer of gypsum of about 1 1/2" thickness. But gypsum did not appear admirable because it could not be waterproofed and so we inquired of an engineer of Dyckerhoff and Widmann, who were engaged with factory buildings of ferro concrete for the Zeiss Works, if he could not suggest a waterproof cement of viscous consistency by a hose similar to that of fire-fighters. If in the interior of your framework we fix to it a wooden shield of suitable spherical curvature, against which we sprinkle cement in thin layers one after another we can avoid the concrete running off the inclined surfaces. Within a few days the cement will be stiff, we take away the shield and you get a fine smooth surface in the interior of the dome which is to be sprinkled by a white colour to represent an ideal surface for the projection.
Basing their design on the thickness ratio of an egg shell to its diameter, Bauersfeld, and Mr. Franz Dischinger and Dr. Ulrich Finsterwalder of Dyckerhoff and Widmann then built the world's first lightweight thin shell concrete dome. Although the firm did not again use the icosahedral dome geometry, the invention was perfected in later structures and made possible clear spans of lighter weight than was previously possible.
In August 1923 the heavens were for the first time accurately reproduced in all their brilliance on the Jena rooftop dome. The stars and individual motions of the planets appeared on the dome's interior and the effect was so startling that even the men who designed the planetarium were astonished, as were early spectators. Newspapers referred to it as the "wonder of Jena".
As the planetarium began to be widely publicized, representatives from large cities in Germany asked Carl Zeiss to sell them planetaria of this kind. This caused the inventors to redesign the first projector which showed only the skies over Munich, to a model that could be used anywhere in the world. 25 of the latter were subsequently built and in May, 1930, the Adler Planetarium opened in Chicago - America's first projection planetarium.
The great circle" principle used in the Jena dome has been in use in the Orient for centuries to weave fish traps, hats and baskets. And the same principle is evident in a remarkable sculpture in China's Summer Palace of a lion holding what appears to be a five frequency geodesic sphere under its claw.
Buckminster Fuller advanced the popularization and commercialization of polyhedral buildings in the United States and is best known for his application of the word geodesic to this type of polyhedral framework.
"Geodesics have an infinite proliferation of possible branches, at the whim of subatomic indeterminism.",
Jack Williamson, The Legion of Time
1 From the Arratus Globe to the Zeiss Planetarium, Helmet, Werner, Publ. Gustav Fischer, Stuttgart, 1957. (Available only from Carl Zeiss, N.Y.)
2 Letter to Shelter Publications from Dr. W. Degenhard, Carl Zeiss, June 19, 1973.
3 James Clayton Lecture: Projection Planetarium and Shell Construction at Institution of Mechanical Engineering, London, May 10, 1957 by Professor Walter Bauersfeld.
Reprinted With Permission from Shelter, © 1973, Shelter Publications, Inc., Bolinas, Calif.