The Coins Of Dionysius

Ernest Bramah was an English author. He published 21 books and numerous short stories and features. His humorous works were ranked with Jerome K Jerome, and W.W. Jacobs, his detective stories with Conan Doyle, his politico-science fiction with H.G. Wells and his supernatural stories with Algernon Blackwood. Bramah created the characters Kai Lung and Max Carrados. Bramah was a recluse who did not give the public details of his personal life. He died at 74 a successful author, having a knowledge of chemistry, physics, law, philosophy, the classics, literature, the occult and ordnance, and being an expert in a branch of numismatics.
This early work by Ernest Bramah was originally published in 1914. 'The Coin of Dionysius' is a mystery short story of a coin and a blind man.
Mr. Carlyle is desperate to solve his current case, and needs an after-hours expert opinion on a certain coin. Why on earth would the coin dealer recommend a blind man?