They are for the most part those followed by the U.S.Forest Service.

In schools equipped with the necessary machinery the instructions will serve to direct the tests; in others a study of the text with reference to the illustrations should give an adequate conception of the methods employed in this most important line of research.
The appendix contains a copy of the working plan followed by the U.S.Forest Service in the extensive investigations covering the mechanical properties of the woods grown in the United States.
It contains many valuable suggestions for the independent investigator.

In addition four tables of strength values for structural timbers, both green and air-seasoned, are included.
The relation of the stresses developed in different structural forms to those developed in the small clear specimens is given.
In the bibliography attempt was made to list all of the important publications and articles on the mechanical properties of wood, and timber testing.

While admittedly incomplete, it should prove of assistance to the student who desires a fuller knowledge of the subject than is presented here.
The writer is indebted to the U.S.Forest Service for nearly all of his tables and photographs as well as many of the data upon which the book is based, since only the Government is able to conduct the extensive investigations essential to a thorough understanding of the subject.

More than eighty thousand tests have been made at the Madison laboratory alone, and the work is far from completion.
The writer also acknowledges his indebtedness to Mr.Emanuel Fritz, M.E., M.F., for many helpful suggestions in the preparation of Part I; and especially to Mr.Harry Donald Tiemann, M.E., M.F., engineer in charge of Timber Physics at the Government Forest Products Laboratory, Madison, Wisconsin, for careful revision of the entire manuscript.
SAMUEL J.RECORD.
YALE FOREST SCHOOL, _July 1, 1914_.
CONTENTS PREFACE.
PART I THE MECHANICAL PROPERTIES OF WOOD Introduction Fundamental considerations and definitions Tensile strength Compressive or crushing strength Shearing strength Transverse or bending strength: Beams Toughness: Torsion Hardness Cleavability PART II FACTORS AFFECTING THE MECHANICAL PROPERTIES OF WOOD Introduction Rate of growth Heartwood and sapwood Weight, density, and specific gravity Color Cross grain Knots Frost splits Shakes, galls, pitch pockets Insect injuries Marine wood-borer injuries Fungous injuries Parasitic plant injuries Locality of growth Season of cutting Water content Temperature Preservatives PART III TIMBER TESTING Working plan Forms of material tested Size of test specimens Moisture determination Machine for static tests Speed of testing machine Bending large beams Bending small beams Endwise compression Compression across the grain Shear along the grain Impact test Hardness test: Abrasion and indentation Cleavage test Tension test parallel to the grain Tension test at right angles to the grain Torsion test Special tests Spike pulling test Packing boxes Vehicle and implement woods Cross-arms Other tests APPENDIX Sample working plan of United States Forest Service Strength values for structural timbers BIBLIOGRAPHY Part I: Some general works on mechanics, materials of construction, and testing of materials Part II: Publications and articles on the mechanical properties of wood, and timber testing Part III: Publications of the United States Government on the mechanical properties of wood, and timber testing ILLUSTRATIONS Frontispiece Photomicrograph of a small block of western hemlock 1.