or not; for, if we dig to the bottom of the earth and find the
foundation--why then we are sure of it. But if we find no foundation, it
is clear that the world stands upon nothing, or, in other words, that it
does not stand at all; therefore, it stands to reason--"

"I beg your pardon," interrupted the Doctor, "but you totally mistake
me; I used the word digging metaphorically, meaning the profoundest
cogitation and research into the nature of things. That is the way in
which we may ascertain whether things are, or whether they are not."

"But if a man can't believe his eyes," said Uncle Tim, "what signifies
talking about it?"

"Our eyes," said the Doctor, "are nothing at all but the inlets of
sensation, and when we see a thing, all we are aware of is, that we have
a sensation of it: we are not aware that the thing exists. We are sure
of nothing that we see with our eyes."

"Not without spectacles," said Aunt Judy.

"Plato, for instance, maintains that the sensation of any object is
produced by a perpetual succession of copies, images, or counterfeits,
streaming off from the object to the organ of sensation. Descartes, too,
has explained the matter upon the principle of whirligigs."

"But does the world exist?" asked the Schoolmaster.

"A good deal may be said on both sides," replied the Doctor, "though the
ablest heads are for non-existence."

"In common cases," said Uncle Tim, "those who utter nonsense are
considered blockheads."

"But in metaphysics," said the Doctor, "the case is different."

"Now all this is hocus-pocus to me," said Aunt Judy, suspending her
knitting-work, and scratching her forehead with one of the needles, "I
don't understand a bit more of the business than I did at first."

"I'll be bound there is many a learned professor," said Uncle Tim,
"could say the same after spinning a long yarn of metaphysics."

The Doctor did not admire this gibe at his favorite science.

"That is as the case may be," said he; "this thing or that thing may be
dubious, but what then? Doubt is the beginning of wisdom."

"No doubt of that," said my grandfather, beginning to poke the fire,
"and when a man has got through his doubting, what does he begin to
build up in the metaphysical way?"

"Why, he begins by taking something for granted," said the Doctor.

"But is that a sure way of going to work?"

"'Tis the only thing he can do," replied the Doctor, after a pause, and
rubbing his forehead as if he wa