STRICTLY PARABOLIC

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This completed line is the curve you seek. It is NOT part of an ellipse. It is NOT part of a circle. It is NOT a hyperbolic. It is a true parabolic curve and you can now use it in the construction of your solar heating unit or cooker. By doubling the drawn curve back over the focal line (pick up point P, swing it over Of, and lay it down again an fP distance on the other side of Of), you can quickly and easily convert the eight-foot-long half-curve you've just drawn into a 16-foot-long full curve. When the focal line of this true parabolic curve is pointed precisely at the sun, ALL the Incoming solar rays which strike the curve and are reflected will focus at f . . . and, believe me, it gets HOT.

OK. Now for some variations. Suppose, for instance, that you want to construct a parabolic reflector which has the same focal length (four feet) of the curve we've just drawn . . . but a smaller diameter. Easy. Starting at the base line fp, just measure up as far as you like, slice off the bottom of the drawing, and keep the rest. (If you cut your drawing as shown in Fig. 7, the remaining portion of the curve can be used to build a collector much like the one shown in Fig. 1a.)

It's a little more complicated-but not really much more difficult-to extend a parabolic "dish" out to some endless dimension . . . while still retaining a specific focal length.

Using the focal length Of as one (1) unit, lay off on the extended line, OX, ANY number of unit lengths that you want. (See Fig. 8 in which, as you'll note, we've tilted our original-Figs. 3 through 7parabolic drawing 90° to the left to give us plenty of drawing space.)

If you'll look at Figs. 8 and 9 you'll note that at the end of each consecutive odd number on line OX, the next vertical line will always be the next EVEN number above the odd . . . while all the inbetween numbers will be fractional. (Example: The first odd numberl-on the base line is followed by a vertical line labeled 2. The second odd number-3-on the base line is followed by a vertical line labeled 4. And so on. And the vertical lines in between 2 and 4-2.82842 and 3.4641-are fractional.)

All right. Note also that the evenly numbered vertical lines (2, 4, 6, etc.)--the ones which separate the odd-numbered unit measurements (1, 3, 5, etc.)--are each longer than the preceding evenly numbered vertical line by the square root of 4 (the square root of 4 is 2, and vertical line 4 is 2 longer than vertical line 2, while vertical line 6 is 2 longer than vertical line 4, etc.).

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