Page:Popular Science Monthly Volume 84.djvu/107

Rh museum. It was constructed, installed and presented to the academy by Mr. La Verne W. Noyes, president of the board of trustees, in order to broaden and to promote the educational and scientific work of the academy.

The material used in constructing the sphere is light galvanized sheetironsheet iron [sic], which has been pressed to the proper curvature and soldered to the equatorial ring and to a smaller ring about the entrance to the sphere. The platform and horizon table are of wood and rest upon a steel frame. The diameter of the sphere is fifteen feet. The weight, exclusive of the platform, is a little more than 500 pounds. This weight is cariedcarried [sic] by a 2″ tube attached to the outside of the sphere along the line of the equator and resting upon three wheels as shown in the cross section view. The two lower wheels carry the greater portion of the weight, but the third and upper wheel, above the door, resists a certain thrust due to the inclined position of the sphere. The stationary platform within the sphere is supported in part by steel trusses resting upon the framework of the museum balcony, and in part by two upright pillars which rest upon the great I beam of the main floor of the museum. This platform carries a circular horizon table, below which the sphere is obscured from view, and above which there is a complete hemisphere on which the stars are represented.

The observer in this sphere is located on the surface of the earth at north latitude 41° 50'. Celestial spheres constructed for localities having other latitudes north or south would be placed at other angles and certain other constellations would be shown. The stars are represented by tiny perforations in the sphere, different sizes being used for stars of different magnitudes. The size

 1-2. South Polar Ring at entrance. 3. Upper Wheel supporting sphere. 4. One of two lower wheels which support the sphere and are propelled by motor. 5. Electric Motor. 6. North Pole of the heavens. 7-8. Horizon Table. 9. Observers' Platform. 10. Switch Board. 11. Electric Wire. 12-13. Ecliptic or apparent path of the sun.