ng of the beetle. How then do you trace
any connection between the boat and the skull--since this latter,
according to your own admission, must have been designed (God only knows
how or by whom) at some period subsequent to your sketching the
_scarabaeus_?"

"Ah, hereupon turns the whole mystery; although the secret, at this
point, I had comparatively little difficulty in solving. My steps were
sure, and could afford but a single result. I reasoned, for example,
thus: When I drew the _scarabaeus_, there was no skull apparent upon the
parchment. When I had completed the drawing I gave it to you and
observed you narrowly until you returned it. _You_, therefore, did not
design the skull, and no one else was present to do it. Then it was not
done by human agency. And nevertheless it was done.

"At this stage of my reflections I endeavored to remember, and _did_
remember, with entire distinctness, every incident which occurred about
the period in question. The weather was chilly (oh, rare and happy
accident!), and a fire was blazing upon the hearth. I was heated with
exercise and sat near the table. You, however, had drawn a chair close
to the chimney. Just as I placed the parchment in your hand, and you
were in the act of inspecting it, Wolf, the Newfoundland, entered, and
leaped upon your shoulders. With your left hand you caressed him and
kept him off, while your right, holding the parchment, was permitted to
fall listlessly between your knees, and in close proximity to the fire.
At one moment I thought the blaze had caught it, and was about to
caution you, but, before I could speak, you had withdrawn it, and were
engaged in its examination. When I considered all these particulars, I
doubted not for a moment that _heat_ had been the agent in bringing to
light, upon the parchment, the skull which I saw designed upon it. You
are well aware that chemical preparations exist, and have existed time
out of mind, by means of which it is possible to write upon either paper
or vellum, so that the characters shall become visible only when
subjected to the action of fire. Zaffre, digested in _aqua regia_, and
diluted with four times its weight of water, is sometimes employed; a
green tint results. The regulus of cobalt, dissolved in spirit of nitre,
gives a red. These colors disappear at longer or shorter intervals after
the material written upon cools, but again become apparent upon the
reapplication of heat.

"I now scrutinized