I was also amazed to read that the window was made of plexiglass: > Observation of the sea outside the craft was conducted directly by eye, via a single, very

I was also amazed to read that the window was made of plexiglass: > Observation of the sea outside the craft was conducted directly by eye, via a single, very tapered, cone-shaped block of Plexiglas, the only transparent substance identified which would withstand the external pressure. https://en.m.wikipedia.org/wiki/Trieste_(bathyscaphe)#Design https://en.m.wikipedia.org/wiki/Trieste_(bathyscaphe)#Design