3 8 Practical Forestry 



Levelling. In the carrying out of drainage operations 

 in connexion with the formation of new plantations, but 

 particularly where the land is nearly level, one of the most 

 necessary implements is the spirit-level or theodolite. There 

 are many other operations, as well as in connexion with 

 draining, where the level and the knowledge of its working 

 are all-important for the forester. Thus in the formation 

 of roads and paths, levelling of ground inequalities, lake 

 and pond forming, etc., the level will be found an almost 

 indispensable instrument in fact, it cannot well be done 

 without. 



Of levelling instruments there are various descriptions, 

 but the simplest of any is the ordinary spirit-level, it being 

 cheap, easily carried about in the pocket, and when erected 

 on a temporary staff will fall in with most requirements in 

 connexion with general forest work. The illustration 

 (Fig. 1) will give a good idea of the simple instrument. 

 When in use the spirit-level is fixed in a frame of brass, the 

 whole being screwed into a staff or support, e. The brass 

 screw, d, serves to adjust the level as required. 



There are two eyesights, a and b, the latter being a 

 square opening, with a fine hair wire crossing it in the 

 middle. 



The relative heights of a series of points are obtained by 

 means of their vertical distances from others which, on the 

 supposition of the earth being a sphere, are equally distant 

 from its centre, and these, which are called level-points, 

 must be found by an instrument constructed for the purpose 

 spirit-level, theodolite, etc. Generally choice is made of 

 any convenient stations, a, b, c, d, on the line of operation 

 (see Fig. 2), and the distances between them are determined 

 by actual ad-measurement. The instrument is then set up 

 and adjusted at, or near, the middle of the interval between 

 every two such points in succession. When the level thus 

 placed, as at /, has been rendered horizontal by means of 

 the adjusting screw, an assistant at each of the stations 

 a and 6, holding what is called a station-staff in a vertical 

 position, moves an index along the staff, up or down, as 

 dictated by the observer of the level, till it coincides with the 



