when the light enters by a window. Supposing a b to be the window and r the body in light and shade, the light to the right hand z will pass the object to the left and go on to p; the light to the left at k will pass to the right of the object at i and go on to m and the two lines will intersect at c and form a pyramid. Then again a b falls on the shaded body at i g and forms a pyramid f i g. f will be dark because the light a b can never fall there; i g c will be illuminated because the light falls upon it.
Light and shadow with regard to the position of the eye (141—145).
141.
Every shaded body that is larger than the pupil and that interposes between the luminous body and the eye will be seen dark.
When the eye is placed between the luminous body and the objects illuminated by it, these objects will be seen without any shadow.
[Footnote: The diagram which in the original stands above line 1 is given on Plate II, No 2. Then, after a blank space of about eight lines, the diagram Plate II No 3 is placed in the original. There is no explanation of it beyond the one line written under it.]
142.
Why the 2 lights one on each side of a body having two pyramidal sides of an obtuse apex leave it devoid of shadow.
[Footnote: The sketch illustrating this is on Plate XLI No 1.]
143.
A body in shadow situated between the light and the eye can never display its illuminated portion unless the