(3) Experiments conducted upon full-sized pieces. The most reliable investigations under this head were either conducted by Professor Lanza, of the Massachusetts Institute of Technology, or else are noted by him in his work, "Applied Mechanics" (ed. 1895, pp. 673-711). They are valuable in that specimens were selected on a commercial rather than on a scientific basis. Professor Lanza claims that such actual pieces are less perfect and show approximately one half the unit strength developed by the more carefully selected smaller specimens. These experiments are characterized as follows: Life-sized Specimens. Miscellaneous Selections as if for Practical Construction. Moisture and Other Data Indefinite. (4) All other experiments. Many experiments have been made from time to time which, while valuable, are not distinguished by any particular method or principle, such as separate the investigations noted in the preceding articles. Data as to selection of specimens, moisture, and other conditions are either incomplete or else absolutely lacking. Such tests are referred to as are noted in works of Hatfield, Trautwein, Lazlett, Rankine, Thurston, and others. Some of these series are exceedingly valuable comparatively. Professor Rankine and Mr. Lazlett experimented principally upon foreign woods. [p006] The figures established by the United States Division of Forestry and alluded to in item 1, page 4, appear, so far as they exist, upon the following pages. Where they do not exist, the leading spaces set apart for them are left vacant for other insertions as preferred. All coefficients are in pounds per square inch. Fractions of pounds in weight and lower figures in coefficients have been omitted as superfluous. It is not always easy to determine the species of living trees, because forms in the forest differ from those in the open, because bark varies with age, and because fruit and leaves of many trees are lacking in the winter. It is easier to tell genus than species--that a tree is an oak, than whether it is a red or a pin oak. Experience is required in this connection. Trees are divided into two general divisions known as Exogens and Endogens.[8] [p007] FOOTNOTES [Footnote 1: Fernow, Introduction to U. S. Forestry Bul. No. 17.] [Footnote 2: Dr. Fernow credits 495 trees to United States (Introduction to U. S. Forestry Bul. No. 17); Prof. Sargent, counting species only and excluding varieties, gives 422 (Silva of North America).] [Footnote 3: "The principal timbers of commerce in the United States are the species known popularly as pine, fir, oak, hickory, hemlock, ash, poplar, maple, cypress, spruce, cedar, and walnut." ("The Lumber Trade of the United States," Treas. Dept., Bureau of Statistics.)] [Footnote 4: Fossils show that many species covered wider ranges than at present.]