Perhaps you've seen the large concrete disc behind the dome of the Hale Telescope?
Yes, this disc is the same approximate weight as the 200-inch mirror and the support cell that it rides on. It was in the Hale Telescope, occupying the same place where the mirror is now, from May, 1940 until October, 1947.
All work on the 200-inch mirror was stopped during World War II, which greatly delayed the arrival of the completed mirror.
Here is a newspaper clipping that shows the dummy mirror installed:
The article dates back to when all work on the Hale Telescope was stopped due to the war and Harley C. Marshall was acting as caretaker.
Harley's role at the observatory dates back to its earliest days. From The Perfect Machine by Ronald Florence:
"By the end of the first year of work on the mountain, cottages had been built for [Superintendent Byron] Hill and a few others with families. Mary Marshall became the schoolteacher. Her husband, Harley Marshall, kept account books and arranged public relations for the tourists who were already finding their way up the mountain to see the world's largest telescope."
As Palomar Observatory's person who is currently in charge of public outreach, Harley Marshall and I have a connection separated by some 70 years.
Florence also describes Marshall's role during WWII:
"On Palomar, with the work crew gone, the buildings were closed. Harley Marshall stayed behind as caretaker, and once a month a small crew came up to the mountain to "exercise" the machinery, checking equipment for corrosion, starting up the oil pumps on the two-hundred-inch telescope, turning the dome, and slewing the drives from one limit to the other to avoid the ravages of inactivity. When they left Marshall was again alone with the machines.From time to time I find myself alone in the dome with the telescope and have the time to stop and consider all that have come before me--those that have worked on the telescope and its mirror, used it to unravel the secrets of the universe, and even those like Harley Marshall who have had a role in telling its story.
"Marshall had been in charge of public relations and visitors before the war. Navy pilots in training at Southern California bases sometimes used Palomar as a navigation point, so Marshall would see planes overhead, but there were no more visitors to the observatory and no press releases. The world had forgotten the perfect machine."
It must have been difficult for Marshall being relatively alone and knowing that the great telescope lay unfinished, not yet able to begin its mission.
Of course the 200-inch telescope was completed. For the last 60 years astronomers have been using it. The story of the telescope is still continuing. Last night it was used for nine and a half hours to probe distant galaxies. Tonight that program will continue and tomorrow night a new set of observers will be here to tackle yet another mystery of the cosmos. If Harley Marshall were here I am sure that he would be happy to know that.