Russell Porter cut-away drawing of Tower Two of the McMath-Hulbert Observatory. Signed and dated Dec 1937.

The 10.5" Cassegrain telescope in Tower One with the attached  spectroheliokinematograph, which is credited with taking the first motion pictures of solar prominences. About 1930.

The three towers of the McMath-Hulbert Observatory, circa 1940.

Finishing construction on Tower Three and the McGregor Building, circa 1939.

Robert McMath in the viewing room at the base of Tower Two, around 1940.