200" Mirror Cast 75 Years Ago Today

75 years ago today, December 2, 1934, Corning Glass Works successfully cast the 200-inch mirror for what would become the Hale Telescope on Palomar Mountain.

I have blogged about this before (see: December 2, 1934 and Pouring Glass: the Movie), but today I wanted to share a photo of the then still molten 200-inch mirror and its creator: physicist George V. McCauley of Corning Glass Works.

It is an interesting photo because the molten glass is hot and glowing, revealing the pattern of the many hollow spots on its underside. Dr. McCauley, or "Mac" as he was called, later described what is shown in the above photo.

"The changing appearance of the disk during this cooling period was fascinating and beautiful. When ladling was completed, the glass above the cores was hotter than the cores themselves and one saw the perfect pattern of the latter in darker contrast with the molten glass. As time passed and the surface glass cooled, while the cores - cooling less rapidly - became the more radiant and were seen as the highlights between the darker ribs of glass, the picture was so beautiful to look upon that it was with regret that it had to be sealed from sight within the two telescoping sections of the annealing kiln."

His description was actually of the view just after they had poured the glass the the 120-inch mirror (now at Lick Observatory), but the Palomar mirror is also honeycombed and went through the same effect. Too bad there aren't any color photos of this.