What is the meaning of "length of my face" in : "Don't be disheartened Mr Pycroft : said my new acquaintance, seeing the length of my face"

I am quoting from The Memoirs of Sherlock Holmes, The Stockbroker’s Clerk by Arthur Conan Doyle.
I gather from the context that that Mr Pycroft is referring to his disappointment by "the length of my face" but I couldn’t find the expression in dictionaries or even on google.