Early Picture Tube Configuration question

[Jetcone]

My nephew just saw a 1939 RCA Television up at Roosevelt's Estate Springwood.
He wanted to know why the tv tube was mounted vertically and a mirror was used for viewing.
The answer he was given was that early television was received upside down and backwards-which is nonsense electronically.
So I went out on the web digging, thinking it might be either the early glass technology and vacuum stability OR early electronics dictating a longer neck to accelerate the beam.
But no one seems to touch on this little fact on the early TV websites.

Before I spread misinformation does anyone here know why the larger screen size (12") CRT's were mounted vertically in 1939??

I know they had long necks but why the long neck when by 1941 they were mounting the picture tubes for direct viewing?

Did they need the length for the deflection technology of the time, or was it because they used electrostatic instead of electromagnetic deflection?

I originally posted in the tubes forum, not seeing this forum. A member pointed me over here thank you.



Thanks
jon