"From a drop of water," said the writer, "a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other. So all life is a great chain, the nature of which is known whenever we are shown a single link of it. Like all other arts, the Science of Deduction and Analysis is one which can only be acquired by long and patient study nor is life long enough to allow any mortal to attain the highest possible perfection in it. Before turning to those moral and mental aspects of the matter which present the greatest difficulties, let the enquirer begin by mastering more elementary problems. Let him, on meeting a fellow-mortal, learn at a glance to distinguish the history of the man, and the trade or profession to which he belongs. Puerile as such an exercise may seem, it sharpens the faculties of observation, and teaches one where to look and what to look for. By a man's finger nails, by his coat-sleeve, by his boot, by his trouser knees, by the callosities of his forefinger and thumb, by his expression, by his shirt cuffs--by each of these things a man's calling is plainly revealed. That all united should fail to enlighten the competent enquirer in any case is almost inconceivable."
"What ineffable twaddle!" I cried, slapping the magazine down on the table, "I never read such rubbish in my life."
"What is it?" asked Sherlock Holmes.
"Why, this article," I said, pointing at it with my egg spoon as I sat down to my breakfast. "I see that you have read it since you have marked it. I don't deny that it is smartly written. It irritates me though. It is evidently the theory of some arm-chair lounger who evolves all these neat little paradoxes in the seclusion of his own study. It is not practical. I should like to see him clapped down in a third class carriage on the Underground, and asked to give the trades of all his fellow-travellers. I would lay a thousand to one against him."
"You would lose your money," Sherlock Holmes remarked calmly. "As for the article I wrote it myself."
"You!"
"Yes, I have a turn both for observation and for deduction. The theories which I have expressed there, and which appear to you to be so chimerical are really extremely practical--so practical that I depend upon them for my bread and cheese."
"And how?" I asked involuntarily.