Another emergency blip

Nasmyth had a theory about how the moon's surface got its 'wrinkles' and used his own hand and an apple to explain.

One of the most memorable self-portraits among many wonderful works on displaying in th his summer's exhibition at the National Portrait Gallery.

A better image here:
https://www.nationalgalleries.org/collection/artists-a-z/n/artist/james-nasmyth/object/back-of-hand-pgp-r-830-1