856 JOURNAL OF R)Ki;STKV 



to each other and facing in opposite directions. One mirror is fixed at 

 one end of the arm, while the other is mounted on a sHde which travels 

 along the arm. Graduations permit a direct reading of the distance 

 between the mirrors. 



The instrument is closely akin to the ordinary calipers in principle, 

 except that for the parallel fixed and movable arms of the calipers are 

 substituted two parallel lines of sight. The direct line of sight passes 

 just above the upper edge of the fixed mirror from eye to one edge of 

 the tree, while the indirect line of sight is reflected in each of the two 

 mirrors to the edge of the tree. Since the two lines of sight are par- 

 allel, the distance between the two mirrors is equal to the diameter of 

 the tree. 



The chief advantages of this instrument are that it is direct reading, 

 does not require the determination of the distance from eye to tree, and 

 hence is not only rapid in use, but may be set for a given diameter, 

 regardless of distance. It is more portable than a pair of calipers of 

 the same range. 



A modification of this type of dendrometer is suggested for timber- 

 survey crews which are using volume tables to a fixed top-cutting limit 

 such as six or eight inches. All that is necessary in such cases is the 

 pair of parallel mirrors, one of which is adjustable, mounted six or 

 eight inches apart on any light base not aflFected too readily by changes 

 of temperature or humidity. 



This instrument would seem to possess considerable merit and de- 

 serves a careful trial at the hands of the profession. A. B. R. 



Instructions for Making Timber Surveys in the National Forests. 

 U. S. Department of Agriculture, Forest Service. Washington, D. C, 

 1917. Pp. 53. 



The purpose of this handbook is to present the policy of the Forest 

 Service for the conduct of timber surveys and to standardize the meth- 

 ods used in the districts to the extent necessary to insure reasonably 

 accurate and uniform results. Conditions in the districts dififer to such 

 a degree that in some respects standardization of methods is not felt to 

 be desirable. It will be necessary, therefore, for each district to issue 

 supplemental instructions to its field officers, based upon the principles 

 herein outlined, regarding methods not standardized by this handbook. 

 This purpose the handbook fulfills admirably. It is clear, concise, and 

 compact; yet it covers all the essentials, such as organization, field 

 methods, progressive steps in timber-survey projects, project report. 



