The Challenge: Make distilled water from seawater using solar power 
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How can we use
this formula to make a parabolic mirror?
To convert this into
actual dimensions used to make the wooden frame to carry the mirror we
can draw up a table. (We will turn the equation around in terms of x rather
than y i.e. x = y^{2} / 4a so by putting in various values of
y we can get corresponding values for x). Y is the distance along from
the center of the mirror and x is the height above the lowest part of
the mirror.
For a mirror with
a focus point onehalf meter (19.7 in.) above the bottom of the mirror we get the
following table:
y (meters) 
y^{2}

y^{2}
/ (4 x a) 
height of
mirror 
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 
0.01
0.04
0.09
0.16
0.25
0.36
0.47
0.64
0.81
1.00 
0.005
0.020
0.045
0.080
0.125
0.185
0.235
0.320
0.405
0.500 
5mm
2cm
4.5cm
8cm
12.5cm
18.5cm
23.5cm
32cm
40.5cm
50cm 
Using these figures
we can make a wooden frame made up of vertical wooden supports fixed to
a flat board. The height of each vertical support is given in the right
hand column of the table for various distances out from the center (y).
A thin wooden sheet was then placed on top to form the parabola on which
to fix the mirror.
Attaching the mirror
