From the article by Carlson we have:

If concave mirrors were employed for imaging, inverted images should appear on drawings.  Do you find some inverted subject on the drawing?

No?  Look carefully please, then go down on this page ....
 

And now?

And now, inverting upside down?

And now?

Solution:

Those people smiling ...  is it only casualty, or a joke from the artist?
 

Now you can play the same game on this other figure, from where some imaginative people already saw astronautic gods.

 

And now some plates from Taube:

And finally an interesting asserting from Carlson. Not related to mirrors, but very interesting too.
 

I interpretated he meant that the lateral directions of the long piece of which he shows two parts are at an angular degree to the engraved deep, which corresponds to the angle between the astronomic and the magnetic north-south directions.

JJL 2000.12.13