74 inch David Dunlap
The 74 inch David Dunlap telescope was the first large telescope with a Pyrex mirror (made by Corning Glass Works in 1933). It was made by Grubb, Parsons and Co. in Newcastle-on-Tyne, England and was dedicated on May 31, 1935. The mirror is one foot thick and weighs two tons. The telescope tube is 30 feet long and the moving parts of the tube and the mount weigh 25 tons.See : http://www.astro.utoronto.ca/~stefan/ddo/instruments.html
An excellent account of the manufacture of this instrument, and much more, can be found here: