James Craven

as Roy

as Dr. Cygnus Layton

as Dr. Bryant

as Commodore Carlson

as Drake

as Captain Hornsby

as Daniels (uncredited)

as Man in Audience

as John Greer

as Vero (uncredited)

as Prof. Millard

as Henry Mills

as Brigadier General (uncredited)

as M. De Treville

as Dr. Bryant

as Swenson (uncredited)

as Stage Actor Playing Philip Mannings

as Commishioner Litchfield

as Prof. Millard

as John Wheeler

as Prof. James Clayton [Chs. 1, 10-12]

as Dr. George Strong

as Mordigan

as Cal Sutton

as Interpreter (uncredited)

as British Major (uncredited)

as Cavalier (uncredited)

as Bismo - Annabella's Friend (uncredited)

as Winsley (uncredited)

as Mr. Winters

as Bidwell

as Ace Diamond

as Dr. Cyrus Layton

as Major Morris

as Commissioner Robert George Hardy [Chs. 5-7]

as Officer (uncredited)

as Thomas (uncredited)

as Lloyd Chapin

as Ship's Radio Man (uncredited)

as Fire Warden

as Ivan Shark

as Guard (uncredited)

as Joseph Rand

as Giovanni (Uncredited)

as Instructor

as Captain in Car (uncredited)

as Dan Slocum

as 'Dandy' Darnell

as Abel Bellamy