“Hartridge, it has come to a show-down between us. I’m giving you fair warning. Once I did you an injustice--or thought I did--but this time you’ve given yourself away. When I get up and around again, I’m going to sift this thing to the ultimate bottom and somebody will be made to sweat blood for what has been done to-night. As matters stand now, you seem to be the man the officers will want first.” Once more the professor smiled. “And yet you can’t say that I have ever wittingly done anything to harm you,” he offered mildly. “That remains to be proved,” was the angry retort. “Meaning to, or not meaning to, you fired that dynamite a little while back; and you certainly have never strained yourself in any effort to help me. You knew that this big vein was here--you have known it all along!” “This time you are not my guest, Mr. Tregarvon, and I may contradict you without blame. I did not know it.” “Then why did you carve the Greek letter _pi_ on those two oak-trees below the glade? Or do you deny that, as well?” “It is you who have found the value of _pi_,” said the one who was under accusation. “I am ashamed to confess that it baffled me. Some three years ago, two strange surveyors acting, as I learned afterward, in the interests of Consolidated Coal, ran many lines over this property of yours, which was then practically abandoned. I had no access to their note-books, of course, so I was obliged to work out my conclusions as best I could from their stakes. One of these conclusions was that the true vein would be found somewhere in this locality. Can you believe me thus far?” “I’m trying to,” said Tregarvon. “Go on.” “It is humiliating to have to acknowledge that, while all the line-running on the part of these strangers pointed to this immediate locality, I could never discover the outcrop. True, I never thought of looking in this particular crevice. But to preserve a record for possible future investigation, I made the marks on the two trees. The distance between the oaks, carefully measured and multiplied by _pi_, or three and the decimal one thousand, four hundred and sixteen, gives the distance around the cliff from the lower oak to the point somewhere below us where the intruding strangers drove their final stake.” Tregarvon heaped more leaves upon the fire, which was threatening to die out. “You are still miles beyond my comprehension,” he complained moodily. “On one hand, you stop at nothing to prevent me from finding out what you have just told me, and on the other you make what appears to be a very worthy and earnest effort to keep me from flinging myself into the maw of Consolidated Coal. How am I to reconcile such things?”