The science of shadow: rays, angles and degrees of darkness
A lettered diagram of shadow-rays with geometric figures on a companion fragment
The verso mounts two fragments. The upper carries geometric figures (circles) and a group of indefinable lines, recorded as invisible before restoration. The lower, blue-primed fragment bears a lettered diagram of the science of shadow: a place is darker the greater the sum of shadow-rays that reach it and the wider the angle they form, so that point a is of double the darkness of point b, while a place struck by more luminous rays is brighter. The construction is worked through the lettered points d, e, f marking the beginning, middle and whole of a shadowed interval.
On this page
The darkest place gathers the most shadow-rays
A note below the first drawing states that a place is more shadowed the greater the sum of shadow-rays by which it is seen. The rule pairs with its converse, that a place is more luminous the greater the sum of luminous rays that strike it back.
Lettered diagram: doubling of darkness
The diagram is labelled m l a b c n o and h i d e f k g. A place struck by a larger angle of shadow-rays is darker: a is of double darkness to b, arising from a double base at equal distance. Point d begins the shadow d f and tinges little at c; d e is its middle, tinging more at b; d f is the whole shadowed interval, wholly tinging place a.
Bodies tinted by neighbouring light and shade
A fragmentary line describes how a surface is tinted by the shadowed and luminous bodies set opposite it, taking on their brightness or darkness. The concern is the modelling of light and shade as it governs the appearance of surfaces.
Geometric figures on the upper fragment
The upper fragment carries circles and a set of indefinable lines, drawn in compass and rule. The editorial note records that this side was invisible before restoration.