that bubble comes from the wake of the House-boat?"

"By my chemical knowledge, merely," replied Holmes. "A merely worldly
vessel leaves a phosphorescent bubble in its wake. That one we have just
discovered is not so, but sulphurescent, if I may coin a word which it
seems to me the English language is very much in need of. It proves, then,
that the bubble is a portion of the wake of a Stygian craft, and the only
Stygian craft that has cleared the Cimmerian Harbor for years is the
House-boat--Q.E.D."

"We can go back until we find the ripple again, and follow that, I
presume," sneered Le Coq, who did not take much stock in the theories of
his great rival, largely because he was a detective by intuition rather
than by study of the science.

"You can if you want to, but it is better not to," rejoined Holmes,
simply, as though not observing the sneer, "because the ripple represents
the outer lines of the angle of disturbance in the water; and as any one
of the sides to an angle is greater than the perpendicular from the
hypothenuse to the apex, you'd merely be going the long way. This is
especially important when you consider the formation of the bow of the
House-boat, which is rounded like the stern of most vessels, and comes
near to making a pair of ripples at an angle of ninety degrees."

"Then," observed Sir Walter, with a sigh of disappointment, "we must
change our course and sail for Paris?"

"I am afraid so," said Holmes; "but of course it's by no means certain as
yet. I think if Columbus would go up into the mizzentop and look about
him, he might discover something either in confirmation or refutation of