369. Draw the right line _BCA_ at pleasure; and upon _C_ as a Center,
with the distance _CA_ or _CB_ as a Radius, describe the Semi-circle
_BDA_; and from the Center _C_ draw _AC_ perpendicular to _BCA_. Then
divide the Quadrants _AD_ and _BD_ each into 90 equal parts or degrees,
and join the right line _AD_ for the Chord of the Quadrant _AD_. This
done, setting one foot of the Compasses in _A_, extend the other to the
different divisions of the Quadrant _AD_; and so transfer them to the
right line _AD_ as in the Figure, and you have a line of Chords _AD_ to
the Radius _CA_. _N. B._ 60 Degrees on the Line of Chords is always
equal to the Radius of the Circle it is made from; as is evident by the
Figure, where the Arch _E_, whose Center is _A_, drawn from 60 on the
Quadrant _AD_, cuts the Chord line in 60 degrees, and terminates in the
Center _C_.
[Sidenote: And of Sines.]
Then, from the divisions or degrees of the Quadrant _BD_, draw lines
parallel to _CD_, which will fall perpendicularly on the Radius _BC_,
dividing it into a line of Sines; and it will be near enough for the
present purpose, to have them to every fifth Degree, as in the Figure.
And thus the young _Tyro_ may supply himself with Chords and Sines, if
he has not a Sector. But as the Sector greatly shortens the work, we
shall describe the projection as done by it, so far as Signs and Chords
are required.
[Sidenote: Fig. II.