In this the second class of rupture by compression, it has been ascertained by experiment that the resistance is in proportion to the area of the surface separated without regard to the form of the surface. Now, in Table I., column H, we have the ultimate resistance to this strain of the several materials named. But to obtain the safe load per inch, the ultimate resistance of the table is to be divided by a factor of safety, of such value as circumstances may seem to require. Generally this factor may be taken at 3. Then to obtain the safe load for any given case, we have but to multiply the given surface by the ultimate resistance, and divide by the factor of safety; therefore, proceed as follows: