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into the board. The plate will consequently turn on this axis as on a
hinge. At the top of the plate, _d_, a small projection of the tin turns
inward, and to this one end of the cord, _m m_, is attached. This cord
passes back from _d_ to a small pulley at the upper part of the board,
and at the lower end of it a tassel, loaded so as to be an exact
counterpoise to the card, is attached. By raising the tassel, the plate
will of course fall over forward till it is stopped by the part _b_
striking the board, when it will be in a horizontal position. On the
other hand, by pulling down the tassel, the plate will be raised and
drawn upward against the board, so as to present its convex surface,
with the words STUDY HOURS upon it, distinctly to the school. In the
drawing it is represented in an inclined position, being not quite drawn
up, that the parts might more easily be seen. At _d_ there is a small
projection of the tin upward, which touches the clapper of the bell
suspended above every time the plate passes up or down, and thus gives
notice of its motions.

[Illustration]

Of course the construction may be varied very much, and it may be more
or less expensive, according to the wishes of the teacher. In the first
apparatus of this kind which I used, the plate was simply a card of


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