The resistance of materials to the force of compression may be considered in several ways. Posts having their heights less than ten times their least sides will crush before bending; these belong to one class: another class is that which comprises all posts the height of which is equal to ten times their least sides, or more than ten times; these will bend before crushing. Then there remains to be considered the manner in which the pressure is applied: whether in line with the fibres, or transversely to them; and, again, whether the pressure tends to crush the fibres, or simply to force off a part of the piece by splitting. The various pressures may be comprised in the four classes following, namely:

1st. - When the pressure is applied to the fibres trans-versely.

2d. - When the pressure is applied to the fibres longitudinally, and so as to split off the part pressed against, causing the fibres to separate by sliding.

3d. - When the pressure is applied to the fibres longitudinally, and on short pieces.

4th. - When the pressure is applied to the fibres longitudinally, and on long pieces.

These four classes will now be considered in their regular order.