134 abstracts: forestry and agriculture 



FORESTRY. — Properties and uses of Douglas Fir. McGarvey Cline 

 and J. B. Knapp. Forest Service Bulletin No. 88. Pp. 75, with 

 plates and diagrams. 1911. 



Douglas fir is perhaps the most important of American woods. It is 

 manufactured in almost every form known to the sawmill operator and 

 much round and hewed timber is used. 



Tests on 8 inch by 16 inch by 16 feet Douglas fir bridge stringers 

 gave an average fiber stress at elastic limit, for all grades, of 4000 pounds 

 per square inch when green, and 4467 pounds per square inch when air- 

 dry; a modulus of rupture of 6000 pounds per square inch when green, 

 and 6327 pounds per square inch when air-dry; and a modulus of elas- 

 ticity of 1,510,000 pounds per square inch when green, and 1,540,000 

 pounds per square inch when air-dry. Tests on smaller pieces, free from 

 defects, to determine the properties of green material, gave an average 

 fiber stress at elastic limit of 5500 pounds per square inch; a modulus of 

 rupture of 8400 pounds per square inch; and a modulus of elasticity of 

 1600 pounds per square inch. Compression parallel to the grain gave 

 a crushing strength at elastic limit of 3600 pounds per square inch. 

 Shearing tests gave an average result of 770 pounds per square inch. 

 Douglas fir varies greatly in quality, the different strength functions rang- 

 ing in value 50 per cent above and below the averages quoted. Tests 

 show that the so-called red and yellow fir have practically the same 

 strength. The mechanical strength of Douglas fir varies directly with 

 dry weight. Pieces which exhibited the greatest strength show usually 

 a rate of growth beween 12 and 16 rings per radial inch. The presence 

 of knots appreciably decreases the strength of green Douglas fir in 

 compression parallel to gram. In beams, the presence of knots affects 

 most the modulus of rupture. The tendency of specifications for Doug- 

 las fir is toward too great severity. Findley Burns. 



AGRICULTURE. — The theory and practice of soil management. Frank 

 K. Cameron, Bureau of Soils. An address before the Michigan 

 Academy of Science, at Lansing, Michigan, April 5, 1911. To 

 appear in its Proceedings. 



The soil possesses individuality, its problems are dynamic rather than 

 static, crop production is a complete function in which all the variables 

 are dependent, and various theoretical considerations which hitherto 

 have not received due attention indicate a greater producing power in 

 our soils than has yet been realized in practice. That high production 

 is desirable in all cases is open to question and involves economic factors 

 that must be considered for particular cases. F. K. C. 



