the substances that form these surfaces,
they are divided into metallic mirrors and glass mirrors--"

"Stop, stop, stop!" interrupted the professor. "Heavens, what a
rattle! We are at the point where the mirrors are divided into
metallic and glass, eh? Now if I should present to you a block of
wood, a piece of kamagon for instance, well polished and varnished,
or a slab of black marble well burnished, or a square of jet, which
would reflect the images of objects placed before them, how would
you classify those mirrors?"

Whether he did not know what to answer or did not understand
the question, the student tried to get out of the difficulty by
demonstrating that he knew the lesson, so he rushed on like a torrent.

"The first are composed of brass or an alloy of different metals and
the second of a sheet of glass, with its two sides well polished,
one of which has an amalgam of tin adhering to it."

"Tut, tut, tut! That's not it! I say to you '_Dominus vobiscum_,'
and you answer me with '_Requiescat in pace!_' "

The worthy professor then repeated the question in the vernacular of
the markets, interspersed with _cosas_ and _abas_ at every moment.

The poor youth did not know how to get out of the quandary: he doubted
whether to include the kamagon with the metals, or the marble with
glasses, and leave the jet as a neutral substance, until Juanito
Pelaez maliciously prompted him:

"The mirror of kamagon among the wooden mirrors."

The incautious youth repeated this aloud and half the class was
convulsed with laughter.

"A good sample of wood you are yourself!" exclaimed the professor,
laughing in spite of himself. "Let's see from what you would define a
mirror--from a surface _per se, in quantum est superficies_, or from a
substance that forms the surface, or from the substance upon which the
surface rests, the raw material, modified by the attribute 'surface,'
since it is clear that, surface being an accidental property of bodies,
it cannot exist without substance. Let's see now--what do you say?"

"I? Nothing!" the wretched boy was about to reply, for he did not
understand what it was all about, confused as he was by so many
surfaces and so many accidents that smote cruelly on his ears, but
a sense of shame restrained him. Filled with anguish and breaking
into a cold perspiration, he began to repeat between his teeth:
"The name of mirror is applied to all polished surfaces--"

"_Ergo, per te_, the mirror i