t
to him.

"I cannot," he said, "delicately explain in so many words what use I
expect to make of this apparel. Nor do I yet know whether I shall have
any use at all for it. That can only be a theoretical speculation
until, within a few more hours, my theory is proven or disproven--and,"
he said, suddenly turning on me, "my theory concerning these invisible
creatures is the most extraordinary and audacious theory ever
entertained by man since Columbus presumed that there must lie
somewhere a hidden continent which nobody had ever seen."

He passed his hand over his protruding forehead, lost for a moment in
deepest reflection. Then, "Have you ever heard of the Sphyx?" he
asked.

"It seems to me that Ponce de Leon wrote of something--" I began,
hesitating.

"Yes, the famous lines in the third volume which have set so many wise
men guessing. You recall them:

"'_And there, alas! within sound of the Fountain of Youth whose waters
tint the skin till the whole body glows softly like the petal of a
rose--there, alas! in the new world already blooming_, THE ETERNAL
ENIGMA _I beheld, in the flesh living; yet it faded even as I looked,
although I swear it lived and breathed. This is the Sphyx_.'"

A silence; then I said, "Those lines are meaningless to me."

"Not to me," said Miss Barrison, softly.

The professor looked at her. "Ah, child! Ever subtler, ever surer--the
Eternal Enigma is no enigma to you."

"What is the Sphyx?" I asked.

"Have you read De Soto? Or Goya?"

"Yes, both. I remember now that De Soto records the Syachas legend of
the Sphyx--something about a goddess--"

"Not a goddess," said Miss Barrison, her lips touched with a smile.

"Sometimes," said the professor, gently. "And Goya said:

"'_It has come to my ears while in the lands of the Syachas that the
Sphyx surely lives, as bolder and more curious men than I may, God
willing, prove to the world hereafter_.'"

"But what is the Sphyx?" I insisted.

"For centuries wise men and savants have asked each other that
question. I have answered it for myself; I am now to prove it, I
trust."

His face darkened, and again and again he stroked his heavy brow.

"If anything occurs," he said, taking my hand in his left and Miss
Barrison's hand in his right, "promise me to obey my wishes. Will
you?"

"Yes," we said, together.

"If I lose my life, or--or disappear, promise me on your honor to get
to the electric launch as soon as possible and make a