Constructive work; . FIGURE While the three classes of levers may be illustrated bymeans of a ruler and triangular prism for a fulcrum it isalso well to encourage older boys to construct a piece ofapparatus by which they may illustrate. In the above fig-ures the power arm may be moved to and fro by removingthe FIGURE XI. In the study of sound Fig. XII. will be of great assist-ance. The turning pegs may be purchased at any departmentor music store for a small sum.

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Keywords: ., bookcentury1900, bookdecade1900, booki, booksubjectmanualtraining