Do a face on white glass in strong outline only: step back, and the face goes to nothing; strengthen the outline till the forms are quite monstrous – the outline of the nose as broad as the bridge of it – still, at a given distance, it goes to nothing; the expression varies every step back you take. But now, take a matting brush, with a film so thin that it is hardly more than dirty water; put it on the back of the glass (so as not to wash up your outline); badger it flat, so as just to dim the glass less than “ground glass” is dimmed; – and you will find your outline looks almost the same at each distance. It is the pure light that plays tricks, and it will play them through a pinhole.”