TOPOGRAPHIC SURVEYING 



US 



measured. The bar ab is placed on any sloping surface, and 

 the arm mn is raised until the bubble t is at the center of the 



FIG. 2 



level tube; the arm will be horizontal and its reading on the 

 graduated quadrant qr will be the required angle. 



The Abney level, shown in Fig. 3, is a combination of a hand 

 level and a clinometer. The spirit level is movable in a vertical 



FIG. 3 



plane, so that when the main tube is given any inclination 

 the level can be turned to a horizontal position and the angle 



