I understand he was a worker in Brazil; more can be found about him here: http://movimentodosirmaos.blogspot.com/p/stuart-edmund-mcnair.html (Chrome should offer to Auto-Translate the page).
I put up a photo of H D'A Champney the other day, one of which was with an 'Eric McNair' who I think is a nephew.
I would definitely liken the photo of McNair from 'Round South America' to the two shown above - just a younger vintage IMHO