IN the first two chapters of Part I. Of this work, the qualities and properties of the ordinary materials of construction are discussed, and also the general nature of the straining actions to which machines are subjected and the principles on which working limits of stress are determined. The third chapter contains a statement of most of the formulae con necting the stress and dimensions of a structure when subjected to tension, bending, torsion, and other straining actions. It is not necessary to repeat what has been there said, but the following tables of the properties of materials are so often wanted for reference that it is desirable to reprint them.