But Leighton was right. Each time the necklace was pulled away it was drawn back to the rock by a strong, invisible force. Repeated trials brought the same result. Leighton's curiosity was excited as it had never been before; but his most careful examination of the strange phenomenon failed to detect anything more than the fact that the substance exerting this unknown force was not stone but something more nearly akin to metal. It was neither so heavy nor so hard as iron. To the touch its surface faintly resembled the adhesive softness of velvet, although a blow from a stone, causing a clear, ringing sound, left not the slightest mark upon it. In the main, this block of metal--or whatever it might be called--was a deep black, tinged with a variegated shade of green that played over it according to the angle at which the ray from a light held above it was reflected. Dark lines of green followed the indentations traversing its surface. Cylindrical in shape, it weighed, according to Leighton's estimate, at least a ton. Imbedded in a deep groove around its center was a rope, measuring two inches in diameter, of pliable fiber, resembling the long lianas that festoon the trees of a tropical forest. This rope lay in a seamanlike coil on the ground, with the further end attached to the transverse beam of the scaffolding overhead. "It is a magnet, nothing else," reiterated Leighton; "a magnet of a kind utterly unknown to science. All we can say is that this black metal has an affinity for gold--unless it turns out that Mrs. Quayle's jewelry is merely iron gilded over." This doubt as to the genuineness of the housekeeper's treasures was promptly denied, however, by Una, who guaranteed their sterling quality. "Let us test the rest of her jewelry," proposed Leighton. To this further demand on her property Mrs. Quayle, wedged in between two rocks on the path where they had left her, too terrified to move, offered only a feeble protest. It mattered little to her, in her present condition, if her bracelets and brooch followed the necklace to their doom. One by one they were, accordingly, removed by Una, who, probably because she was less excitable than Miranda--and because, too, she had profited by his untoward experience in the same undertaking--was able to handle these pieces of jewelry without mishap. The force with which they were pulled towards the Black Magnet, however, and the tenacity with which they stuck to it, gave ample evidence that they answered to the same influence that still held the necklace. "That is enough," said Leighton triumphantly. "The thing is proved. This is a gold magnet. If we lived in the Middle Ages we would call it the Philosopher's Stone. The theory that such a substance exists has attracted scientists who were more given to dreaming than practical observation. In this age we have neither looked for it nor believed in the possibility of its existence. And here it is!"