A Treatise on Painting
by Leonardo da Vinci, translated by John Francis Rigaud
Of studying in the Dark, on first waking in the Morning, and before going to sleep
3995917A Treatise on Painting — Of studying in the Dark, on first waking in the Morning, and before going to sleepJohn Francis RigaudLeonardo da Vinci

Chap. XXI.Of studying in the Dark, on first waking in the Morning, and before going to sleep.

I have experienced no small benefit, when in the dark and in bed, by retracing in my mind the outlines of those forms which I had previously studied, particularly such as had appeared the most difficult to comprehend and retain; by this method they will be confirmed and treasured up in the memory.