Why is the word "in" capitalized in A Study In Scarlet?

[wordplay]

I'm reading the Sherlock Holmes stories and the first book is A Study In Scarlet, and in the first chapter of the book titled Mr. Sherlock Holmes, the word "in" fully capitalized. Why is that?

If this is the not the right forum for such questions, can anyone suggest a forum where I can ask such questions. Thanks