The different kinds of light afforded in cellars by various forms of windows. The least useful and the coldest is the window at a. The most useful, the lightest and warmest and most open to the sky is the window at b. The window at c is of medium utility.
[Footnote: From a reference to the notes on the right light for painting it becomes evident that the observations made on cellar-windows have a direct bearing on the construction of the studio-window. In the diagram b as well as in that under No. 510 the window-opening is reduced to a minimum, but only, it would seem, in order to emphasize the advantage of walls constructed on the plan there shown.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.