The minutes moved tardily on, and as the meridian hour approached, Beatrice said:—
"Have you noticed how the shadow cast by the stone creeps slowly along over the face of the ground? This hillock could easily be turned into a giant sun-dial."
"You echo my thoughts, Miss Ravengar. And it seems to me that this shadow will furnish us with the clue we want."
"You mean that the shadow of the stone will fall on the very spot where the entrance is?"
"Not quite: for in that case the shadow would be an uncertain guide, varying with the sun's altitude at the different seasons: and, besides, you will notice that the shadow is many yards from the foot of the tumulus. It is not probable that the secret entrance lies so far off. No: my idea is this. Connect the oft-carried throne and its shadow with an ideal line, and near the point where this line cuts the base of the hillock will be found the mouth of the passage. It is the noontide hour now," continued Idris, rising. "We will put a little pile of stones to mark the spot where the apex of the shadow falls—so," he added, suiting the action to the word. "Now all we have to do is to walk from this point to the foot of the hillock, keeping in a bee-line with that piece of basalt on the summit, and, unless I err, we shall hit upon the entrance."
Speaking thus, Idris began his experiment. When he had come to the foot of the hillock, Beatrice observed with surprise that the thick, heavy walking-stick carried by him was in reality the receptacle for a long and stout sword. This weapon he pushed into the side of the hillock at the spot touched by the imaginary line.
After a series of probings, begun on a level with the ground and continued in an upward direction, Idris paused with a gleam of excitement on his face. Changing the direction, he resumed his probing, moving horizontally to the right and stopping again. Then he continued the movement, this time coming downward, so that the course of his sword had described three sides of a rectangle.
"Miss Ravengar," he cried, in a voice of emotion, "I have found the entrance! As I live, I have found it! Here, hidden within the soil, are two stone blocks a little distance apart, with a third resting crosswise upon them, the three forming a kind of doorway. We have only to remove the earth overlying them, and we shall find a hollow passage beyond."
Beatrice's cheek coloured with pleasure as Idris continued:—
"Miss Ravengar, you have proved yourself a valuable auxiliary. But for your explanation I might still be puzzling my mind as to the meaning of 'the oft-carried throne.' I offer you a somewhat problematic reward. Whatever spoil is found within shall be divided equally between us."