the bit we look at. If you cut the screen loose, you can move the hole about over the picture and get an idea of the whole in that way. It is a tedious process,

but it was the only way astronomers had of examining a large object like this when they used their eyes and had not learnt to take photographs: and you cannot wonder that they got imperfect ideas of them. The eminent astronomer Trouvelot drew a picture of this same nebula,