Atlantic, Niagara and Underground

“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." (Sherlock Holmes)

"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." (
Dr John Watson)
See also: