GR translation: like Ochsen-Augen in Grandmother’s day

[Mike Jing]

V751.14-19, P766.7-12   He’s been given a window of artificial sapphire,
four inches across, grown by the IG in 1942 as a mushroom-shaped boule, a
touch of cobalt added to give it a greenish tint—very heat-resistant,
transparent to most visible frequencies—it warps the images of sky and
clouds outside, but pleasantly, like Ochsen-Augen in Grandmother’s day, the
days before window-glass. . . .

The *Companion* claims that Ochsen-Augen are "round dormer windows, made of
isinglass." However, isinglass windows are made of flat sheets of mica,
which do not distort images, at least not in the same way as it is expected
here. Several sources seem to indicate that it actually refers to a kind
of small convex mirror, see

https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Mirror

https://www.gutenberg.org/files/48152/48152-h/48152-h.htm

for example. And I couldn't find any supporting evidence
for Weisenburger's claim.

Anyone knows if the *Companion* is mistaken on this one?