Source edition for Project Gutenberg Ebook #50325 (see), whose immediate source is the Google Books scan of a copy at the Bavarian State Library.
half-title page (all caps):
-- "Vol. CXV."
-- "In One Volume."
(The first edition was a standard three-volume.)
title page (all caps):
-- "Copyright Edition for Continental Circulation."
WorldCat record OCLC 837052249 reports size 22 cm.
A small book in paper covers is expected, as the uniform format at least from 1881 to 1909, and the inexpensive format thereafter.
British Library record BL 009987358 reports 16 cm.
Other BL and OCLC records report size octavo.