The Hounds of Tindalos by Frank Belknap Long

"I'm glad you came," said Chalmers. He was sitting by the window and his face was very pale. Two tall candles guttered at his elbow and cast a sickly amber light over his long nose and slightly receding chin. Chalmers would have nothing modern about his apartment. He had the soul of a medieval ascetic, and he preferred illuminated manuscripts to automobiles and leering stone gargoyles to radios and adding-machines.

As I crossed the room to the settee he had cleared for me I glanced at his desk and was surprised to discover that he had been studying the mathematical formulae of a celebrated contemporary physicist, and that he had covered many sheets of thin yellow paper with curious geometric designs.