The Adventures of Sherlock Holmes
How we cite our quotes:
"You have an answer to everything. But how on earth do you deduce that the gas is not laid on in his house?"
"One tallow stain, or even two, might come by chance; but when I see no less than five, I think that there can be little doubt that the individual must be brought into frequent contact with burning tallow – walks upstairs at night probably with his hat in one hand and a guttering candle in the other. Anyhow, he never got tallow-stains from a gas-jet. Are you satisfied?"
"Well, it is very ingenious," said I, laughing (Carbuncle.45-7).
This section of deduction belongs to a long chain in which Holmes also reasons that the poor owner of this hat has lost the love of his wife. Besides being a pretty amazing performance of the kind of deductive reasoning Holmes so adores, this scene is also interesting for Watson's frequent expressions of amazement and disbelief. He's basically egging Holmes on, giving him a plot-based reason for why he would be talking through the identity of the owner of an old hat in such detail: Holmes does this because Watson wants him to, because he asks Holmes, "how on earth do you deduce?"
"You must not fear," said he soothingly, bending forward and patting her forearm. "We shall soon set matters right, I have no doubt. You have come in by train this morning, I see."
"You know me, then?"
"No, but I observe the second half of a return ticket in the palm of your left glove. You must have started early, and yet you had a good drive in a dog-cart, along heavy roads, before you reached the station."
The lady gave a violent start and stared in bewilderment at my companion (Band.12-6).
This scene takes place when Holmes first meets Helen Stoner, the extremely fragile heroine of "The Speckled Band." Her physical expression of surprise at Holmes's deductions helps emphasize how unusual he is. But it also gives the scene a material, realistic quality that Conan Doyle seems to be striving for all the time in these stories.