For  example,  eight  (Fig.  196).     When  the  number  of  parts  is  a

power  of  2,   the  division

A       '        D — -^ Q ' ' ' ^  is  best  performed  by  suc-

Fig.  196.  cessive  bisections.    Thus,

make  AB  a  transverse
distance  between  10  and  10,  then  the  distance  between  5  and
5  will  give  AC  =  half  AB.  Then  make  the  transverse  distance
between  10  and  io  =  AC,  the  distance  between  5  and  5  will
then  give  AD  =  one  quarter  of  AB.  By  repeating  the  operation
each  quarter  will  be  bisected,  and  the  given  line  divided  into
eight  equal  parts  as  required.
INSTRUMENTS    FOR   MEASURING   ANGLES,   ETC.     97

When  the  number  of  divisions  are  unequal,— for  example,
seven  (Fig.  197), — make  the  transverse  distance  between  7  and

I  1  I  I  1  I  '  I

A  c        B

Fig.  197.
7  equal  to  the  given  line  AB  ;  then  take  the  distance  between
6  and  6,  which  will  give  AC.  The  distance  CB  will  then  divide
the  line  into  seven  equal  parts.
139.    How  to  use  the  sector  as  a  scale.
Example. — A  scale  of  1  inch  equals  5  chains.  Take  one  inch
on  the  dividers,  and  open  the  sector  till  this  forms  a  transverse
distance  between  5  and  5  on  each  line  of  lines  ;  then  the  corre-
sponding distances  between  the  other  divisions  and  subdivisions
will  represent  the  number  of  chains  and  links  indicated  by
these  divisions  :  for  instance,  the  distance  between  4  and  4
represents  4  chains,  6.5  =  6  chains  50  links,  Z-7="3  chains  70
links,  etc.
Note. — i  chain  is  equal  to  100  links.
140.    To  construct  a  scale  of  feet  and  inches,  in  which  2^  inches  shall
represent  20  inches.
