Thus if you draw a place with a window looking northwards, and let this be s f , you will see a line starting from the horizon to the east, which, touching the 2 angles of the window o f , reaches d ; and from the horizon on the west another line, touching the other 2 angles r s , and ending at c ; and their intersection falls exactly in the middle of the opening and thickness of the window. Again, you can still better confirm this proof by placing two sticks, as shown at g h ; and you will see the line drawn from the centre of the shadow directed to the centre m and prolonged to the horizon n f .
[Footnote: B here stands for cerchio del' orizonte tramontano on the original diagram (the circle of the horizon towards the North); A for levante (East) and C for ponete (West).]
139.
Every shadow with all its variations, which becomes larger as its distance from the object is greater, has its external lines intersecting in the middle, between the light and the object. This proposition is very evident and is confirmed by experience. For, if a b is a window without any object interposed, the luminous atmosphere to the right hand at a is seen to the left at d. And the atmosphere at the left illuminates on the right at c, and the lines intersect at the point m.
[Footnote: A here stands for levante (East), B for ponente
(West).]
140.
Every body in light and shade is situated between 2 pyramids one dark and the other luminous, one is visible the other is not. But this only happens