"It was while reading 'The Sign of the Four,' which I had procured at the Public Library, that I made the first discovery.The crime therein narrated had been committed in such a singular manner that it at once attracted my attention.The victim had apparently been murdered without anyone having either entered or left the room.In this respect it was like the problem we are trying to solve.Might not this book, I said to myself, have suggested to your father's assassin the course he pursued.I concluded to go to the library and ask for a list of the names of persons who had taken out this book for a few months prior to your father's death.I was fully aware that the chance of my learning anything in this way was very slight, In the first place; I reasoned that it was not especially likely your father's murderer had read 'The Sign of the Four,' and, in the second place, even if he had, what assurance had I that he had read this particular copy of it? Notwithstanding this, however, I felt impelled to give my synthetical theory a fair experimental trial.I was informed by the Library attendants that the book had been much read, and given the list of some twenty names of persons who had borrowed the book during the time I had specified.With these twenty-odd names before me, I sat down to think what my next step should be.I went carefully over this chain of reasoning link by link.'I wish to find a certain murderer, and haveadopted this method in the hope that it may help me.If I derive any assistance at all from it, it will be because my man has read this particular copy of this work; therefore, I may as well assume at the start that among these twenty-odd names is that of the man I want.Is there any possibility of this crime having been committed by a woman?' was my next question, and my answer was, 'Yes, a possibility, but it is so decidedly improbable that I may count it out for the time being.' Accordingly, I set aside all the female names, which cut my list down to eighteen.Several of the applicants had only signed the initials of their given names, and the attendant, copying them from the slips, had done likewise; so I was obliged to go to the registration clerk to determine this question of sex, and, while there, I also ascertained the age of each applicant - that is, of all but two.The registrar could give me no information regarding J.Z.Weltz, or B.W.Rizzi.When I told him that one of the clerks had copied the names for me from application slips, he informed me that if I would go back to her I would undoubtedly find she had taken the two last-mentioned names from the green slips used in applying for books for hall use, as neither J.Z.Weltz nor B.W.Rizzi was a card-holder.
"I decided to let these two names rest a while, and to give my attention to the others.After careful deliberation I felt reasonably sure your father's assassin could not fail to be a man of mature judgment and extraordinary cunning, probably a man past middle life - at all events, I could safely say he was over twenty-one years of age.Proceeding upon this assumption my list was reduced to ten names.But how should I further continue this process of exclusion? This was the question which now confronted me.I could think of but one way, apart from personally making the gentlemen's acquaintance, which I did not then wish to do, and that was to ascertain what other books they had borrowed immediately before and after they had read 'The Sign of the Four.' This was the course I determined to pursue.
"If you ask me why I so persistently followed an investigation, a successful outcome of which anyone must recognise would be little short of miraculous, I can only say that I felt impelled to do so.Perhaps the impulse was due to my habit of testing patiently and thoroughly each newtheory which impresses me as having any degree of probability, and perhaps it was due to something else - Cleopatra, perhaps, eh, Doctor? - I don't know.I determined, however, to thoroughly satisfy myself regarding these ten men.I made a careful list, with the assistance of an attendant, of ten books taken by each man, five taken just prior to 'The Sign of the Four,' and the other five just following it.I made no deductions until the list was completed, although I began to see certain things of interest as we worked upon it.At length the whole hundred titles were spread before me, and I sat down to see what I could make of them.I purposely reserved consideration of the books borrowed by Weltz and Rizzi until the last, because I had been able to learn nothing of them, and considered, therefore, that they were the most difficult persons in the list about whom to satisfy myself.I found the other eight exhibited no system in their reading.One had read - I think I can remember the books in the order in which they were borrowed - 'Thelma,' 'Under Two Flags,' 'David Copperfield,' 'The Story of an African Farm,' 'A Study in Scarlet,' 'The Sign of the Four,' 'The Prisoner of Zenda,' 'The Dolly Dialogues,' 'The Yellow Aster,' 'The Superfluous Woman,' and 'Ideala.' This is a fair sample of the other seven.Not so, however, with Messrs.Weltz and Rizzi.The reading of these men at once impressed me as having a purpose behind it.
"I will read you a list of the books taken by Weltz and Rizzi, just to see what you will make out of it:
WELTZRIZZI
I."Lecons de Toxicologic," 1."Traite de Toxicologic," par M.Orifia.par C.P.Galtier.
2."The Poisons of Asps and 2."The Poisons of Asps and Other Stories," by Florence Other Stories," by Florence Marryat.Marryat.
3."A Practical Essay on3."A Practical Essay on Cancer," by C.T.Johnson.Cancer," by C.T.Johnson.
4."The Sharper Detected4."The Sharper Detectedand Exposed," by R.Houdin.and Exposed," by R.Houdin.
5."The Sign of the Four,"5."The Sign of the Four,"by A.
Conan Doyle.by A.Conan Doyle.
