37 



distributed over the entire length of the beam, the beam would hold twice as much, 

 provided it did not fail in longitudinal shear. Short, deep beams are especially liable 

 to fail in longitudinal shear. In order to insure safety in practice, beams are seldom 

 allowed to carry more than one-sixth of their breaking load. 



Computing- 



In order to facilitate the construction of forest tables, supervisors are requested to 

 have all forest measurement data of general value secured by forest assistants or 

 rangers, such as stem analyses, heights, valuation surveys, etc., sent in to the office 

 for the construction of tables by the Section of Computing. If the original data are 

 desired for filing by the supervisor, copies should be sent in. 



By combining data gathered by different men relating to the same species under 

 the same growth conditions, the useless duplication of measurements will be avoided, 

 and uniformity and greater accuracy will be attained in the construction of tables. 



Form Factors of National Forest Trees 



From a large number of accurately measured trees the Forest Service has estab- 

 lished the average form factor for lodgepole pine in Montana to be 0.53, with a range 

 of from 0.58 for 6-inch trees to 0.42 for 22-inch trees. Douglas fir in Idaho and Wyo- 

 ming varies from 0.58 for 10-inch trees to 0.40 for 40-inch trees, with an average of 

 0.49 for merchantable trees. The average form factor of western yellow pine in the 

 Black Hills is 0.53, with but little variation. In the Sierras of California it is 

 0.42, with a range from 0.45 to 0.39 as extremes a very small variation. In other 

 words, western yellow pine in the Black Hills would be expected to give a 



CO 



scale of / 9 of the scale of a tree of the same dimension in the sugar pine-yellow r pine 



belt of California. This would be more than -. more in the former region, and is 



further greatly increased by the closer cutting in the Black Hills, where better local 

 markets are found for the lower grades of lumber. 



Studies of National Forest Timbers 



The study of the properties, uses, and markets of the timbers found in the National 

 Forests will be continued during the present season. Western larch, amabilis fir, 

 incense cedar, and several other of the less used species will form the basis of this 

 study. Tests will be made to determine the streDgth of the various species. These 

 tests will supplement the field study, the object of which will be to discover the 

 best uses and markets for these woods. 



OFFICE OF WOOD PRESERTATION. 



Loblolly Pine Cross- Arms 



The field work in the experimental treatment of loblolly pine cross-arms has 

 recently been completed. In the fall of 1905 a cooperative agreement was entered 

 into between the Forest Service and the American Telephone and Telegraph Com- 

 pany with the object of devising a system for preserving cross-arms and similar 

 classes of material which would insure more desirable and economical results than 

 were being obtained under the existing conditions. Timber cut during each month 

 "of the year was collected at the yards of a Norfolk ( Va. ) creosoting company, graded 

 into three classes in accordance with the relative amounts of heartwood and sap- 



