The genesis of a significant scientific idea is a miracle- the gradual increase in clarity from the fog to the realisation that the truth was as obvious as day. This is a wonderful anti-climax, and anyone who has experienced it will be find Holmes' illustration in "The Dancing Men" uncanny: Holmes had been seated for some hours in silence with his long, thin back curved over a chemical vessel in which he was brewing a particularly malodorous product. His head was sunk upon his breast, and he looked from my point of view like a strange, lank bird, with dull gray plumage and a black top-knot. "So, Watson," said he, suddenly, "you do not propose to invest in South African securities?" I gave a start of astonishment. Accustomed as I was to Holmes's curious faculties, this sudden intrusion into my most intimate thoughts was utterly inexplicable. "How on earth do you know that?" I asked. He wheeled round upon his