| 139 | 140 | 141 | 142 | 143 |
| 1 | 306 | 613 | 919 | 1225 |
|
faces a b; and m n faces c d; the body in the middle having a
larger quantity of light than those at the sides is lighted from a
point much below its centre, and thus the shadow is shorter. And the
pyramid g 4 goes into l y exactly as often as a b goes into e
f. The axis of every derivative shadow passes through 6 1/2
[
Footnote 31: passa per 6 1/2 (passes through 6 1/2). The meaning
of these words is probably this: Each of the three axes of the
derived shadow intersects the centre (mezzo) of the primary shadow
(ombra originale) and, by prolongation upwards crosses six lines.
This is self evident only in the middle diagram; but it is equally
true of the side figures if we conceive of the lines 4 f, x n v
m, y l k v, and 4 e, as prolonged beyond the semicircle of the
horizon.] and is in a straight line with the centre of the primary
shadow, with the centre of the body casting it and of the derivative
light and with the centre of the window and, finally, with the
centre of that portion of the source of light which is the celestial
hemisphere, y h is the centre of the derived shade, l h of the
primary shadow, l of the body throwing it, l k of the derived
light, v is the centre of the window, e is the final centre of
the original light afforded by that portion of the hemisphere of the
sky which illuminates the solid body.
[Footnote: Compare the diagram on Pl. IV, No. 3. In the original
this drawing is placed between lines 3 and 22; the rest, from line 4
to line 21, is written on the left hand margin.]
141
Page
Quick Jump
|