“Yes, I have been guilty of several monographs. They are all upon technical subjects. Here, for example, is one ‘Upon the Distinction between the Ashes of the Various Tobaccos.’ In it I enumerate a hundred and forty forms of cigar, cigarette, and pipe tobacco, with coloured plates illustrating the difference in the ash. It is a point which is continually turning up in criminal trials, and which is sometimes of supreme importance as a clue. If you can say definitely, for example, that some murder had been done by a man who was smoking an Indian lunkah, it obviously narrows your field of search. To the trained eye there is as much difference between the black ash of a Trichinopoly and the white fluff of bird’s-eye as there is between a cabbage and a potato.”[The Sign of Four]
“나는 시가, 담배, 파이프 담배 140종을 열거하고, 재의 차이를 보여주는 컬러 도판을 첨부했지. 이는 형사 재판에서 끊임없이 등장하는 중요한 단서이며, 때로는 결정적인 증거가 되기도 했네.” 그의 논문에 대한 자평이다. 그의 이러한 실력은 실제로 보스콤 계곡 미스터리(The Boscombe Valley Mystery)에서 어느 정도 입증되기도 했다.