LESSON 10 
LEVELING 
HE student should now learn the simpler methods 
of leveling, and the present exercise is intro- 
duced for this purpose. 
Definitions 
A level line is a line parallel to the surface of 
a smooth body of water, i.e., parallel to the gen- 
eral surface of the earth. It is therefore a curved line. 
A horizontal line is a line parallel to the plane of the horizon; 
or it is a straight line tangent to a level line at any point, that is at 
right angles to a vertical line. 
A level is an instrument, with or without a telescope, fixing a 
line of sight (line of collimation) by means of which differences of 
elevation may be determined. It will be understood that the line 
run by a level is not level but horizontal. 
Equipment 
For the business now in hand it is not at all necessary to use 
any elaborate engineering instruments. The farm or drainage level 
is a very simple instrument, consisting of a cheap telescope (some- 
times a tube with glass windows and no lenses) mounted on a light 
tripod or set up on a jacob-staff. (See Figure 18.) 
A hand level is a tube, with or without lenses, in which 
is mounted a horizontal hair, thus fixing a line of sight. The in- 
strument is held in the hand while making observations. 
For all operations which give any reasonable degree of exact- 
ness it is necessary to have also a leveling-rod, which is essentially 
a straight wooden rod usually marked conspicuously in feet, tenths 
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