TEXTBOOK OF LANDSCAPE GARDENING 
it should be at least 75 feet from a railroad. A large pocket knife 
will affect the needle if within a foot or so of it. 
When possible the instrument may be rested on the top of a 
post or stick or even on the ground. 
If the instrument has sight vanes the N.—S. line should be 
brought to bear on the object whose direction is desired by holding 
the instrument nearly up to the level of the eye and sighting through 
the vanes. When the needle has come to rest it should be care- 
fully clamped and the direction read. The average of two or three 
readings will be more accurate than a single one. 
If there are no sight vanes the instrument must be held at a 
lower position and the N.-—S. line directed by estimation toward the 
object sought. When the needle has come to rest its direction may 
be read or the average of the swing may be taken before it comes to 
rest. It may be helpful in directing the N.-—S. line to hold the in- 
strument so that the thumbs meet at S. and the first fingers at N. 
or to lay a pencil across over the N.—S. line. 
The prismatic compass should be held close to the eye and the 
hands pressed against the face to steady it. Occasional pressure on 
the stop will bring the needle to rest more quickly or the average 
swing may be taken rather than to wait for the needle to come to 
complete rest. 
In using the prismatic compass the reading is taken at a fixed 
point on the compass box on the line of sight near the eye. 
In using the box or pocket compass keep the S. point of the dial 
toward you and always read the N. end of the needle, recording 
first S. or N. (whichever is nearest the N. end of the needle) then 
the degrees indicated, then if E. and W. are printed in reversed 
positions record whichever is nearest the N. end of the needle. If 
however they are printed in correct positions record the opposite. 
When the dial of a box compass is graduated in azimuth clock- 
wise from N. read the N. end of the needle and plot counter-clock- 
wise. 
38 
