The power of the ring

This is from "The Five Chameleons", just a couple of chapters after the description of the sanctum.

Slowly, The Shadow drew the black glove from his left hand, to reveal the long, white fingers. Martha stared in amazement at the resplendent gem which she saw. Its marvelous changing hues were reflected clearly, even in the dim light. "This girasol," said the spectral voice, "is the symbol of The Shadow. Few have ever known its significance. You are one. "He who wears this stone - like which there is no other - is The Shadow. No matter what his guise may be, he is The Shadow. Tell none what I have told you!" "I understand," said Martha breathlessly. "I shall remember. No one else shall know." As the girl stared at the gem, she lost all sense of material forms about her. The effect of the glowing jewel was hypnotic. The figure of The Shadow seemed to melt into darkness. The white hand disappeared. Only the changing girasol, with its hues of ultramarine and crimson, sparkled before her eyes. The impression was fading. The glorious gem was melting away. Martha reached forward to clutch it. Her hands closed on space as the colors no longer remained. The girl looked about her. She was alone in the room. Her eyes had retained the impression of the wavering colors, and she had fancied that The Shadow had remained. Now all was like a dream. Only the paper in her hand stood as proof of The Shadow's presence. Had she imagined the singular conversation which had taken place? It was possible that such was the case; yet Martha could not dismiss the semblance of reality. She was sure that The Shadow had been in this very room. She believed that he would aid her. She felt positive that he would return; that soon, again, she would see the mystic gem that was his token.