old man before-mentioned
held in his hands.

The one held in the left hand resembled a white porcelain slate, only
being much larger than those in common use. It was nearly twenty inches
square, and was divided by mathematical lines into thirty-six
compartments. It was covered over with a thin crystal, resembling glass,
which is found in great quantities in the neighboring mountains, and is
perfectly transparent. The crystal was raised about the one eighth of an
inch from the surface of the slate, and allowed a very fine species of
black sand to move at will between them. The instrument carried in the
right hand resembled the bow of a common violin, more than anything
else. The outer edge was constructed of a beautiful yellow wood,
polished, and bent into the arc of a quarter circle; whilst a mass of
small cords, made of the native hemp, united the two ends.

The method of using the bow was this: The slate was shaken violently
once or twice, so as to distribute the black sand equally over the white
surface, and then the bow was drawn perpendicularly down the edge of the
slate, very rapidly, so as to produce a quick whistling sound. The
effect produced upon the grains of sand was truly wonderful to the
uninitiated in the laws of acoustics. They arranged themselves into
peculiar figures, sometimes in the form of a semicircle, sometimes into
that of a spiral, sometimes into a perfect circle, or a cone, or a
rhomboid, or an oval, dependent entirely upon two things: first, the
place where the slate was held by the left hand; and second, the point
where the bow was drawn across the edge. As the slate was subdivided
into thirty-six compartments, by either one of which it could be held,
and as there was a corresponding point, across which the bow could be
drawn, there were seventy-two primitive sounds that might be produced by
means of this simple contrivance. Each of these sounds inherently and
necessarily produced a different figure upon the slate, and there were
consequently just seventy-two initial letters in the Aztec alphabet.

The mode of instruction was extremely simple. A word was pronounced by
the aged teacher at the front of the stage, written upon his slate,
exhibited to the scholar at the black tablet, and by him copied upon it.
The whole class then drew down their bows, so as to produce the proper
sound, and the word itself, or its initial letter, was immediately
formed upon the slate.

After the seventy-two