He was silent a moment. Then he spoke with unusual seriousness.
"Markham, take my advice and don't bother with these side-issues. I'm telling you the girl had no part in the murder. Let her alone,—you'll be happier in your old age if you do."
Markham sat scowling, his eyes in space.
"I'm convinced that you think you know something."
"Cogito, ergo sum," murmured Vance. "Y' know, the naturalistic philosophy of Descartes has always rather appealed to me. It was a departure from universal doubt and a seeking for positive knowledge in self-consciousness. Spinoza in his pantheism, and Berkeley in his idealism, quite misunderstood the significance of their precursor's favorite enthymeme. Even Descartes' errors were brilliant. His method of reasoning, for all its scientific inaccuracies, gave new signif'cation to the symbols of the analyst. The mind, after all, if it is to function effectively, must combine the mathematical precision of a natural science with such pure speculations as astronomy. For instance, Descartes' doctrine of Vortices"
"Oh, be quiet," growled Markham. "I'm not insisting that you reveal your precious information. So why burden me with a dissertation on seventeenth-century philosophy?"
"Anyhow, you'll admit, won't you," asked Vance lightly, "that, in elim'nating those disturbing cigarette butts, so to speak, I've elim'nated Miss St. Clair as a suspect?"
Markham did not answer at once. There was no doubt that the developments of the past hour had
