We have seen that a corporeal surface appears as black if light striking it is totally absorbed by it. Thus, wherever our eye is met by the colour black, our visual ray is engaged in a process whereby light disappears from physical space. Now we need only bring this process into consciousness - as we have tried to do before in similar instances - to realize that what happens here to the visual ray is something similar to what it undergoes when it is directed from the earth into cosmic space.