b he wrote dirivatiuo and at d deriuatiua (derived).]
Experiments on the relation of light and shadow within a room (137—140).
137.
SHOWS HOW LIGHT FROM ANY SIDE CONVERGES TO ONE POINT.
Although the balls a b c are lighted from one window, nevertheless, if you follow the lines of their shadows you will see they intersect at a point forming the angle n.
[Footnote: The diagram belonging to this passage is slightly sketched on Pl. XXXII; a square with three balls below it. The first three lines of the text belonging to it are written above the sketch and the six others below it.]
138.
Every shadow cast by a body has a central line directed to a single point produced by the intersection of luminous lines in the middle of the opening and thickness of the window. The proposition stated above, is plainly seen by experiment.