It is the same with the well-known theory of projection. The problem of the _physicist_ is, to seek the luminous object-point of a point imaged on the retina of the eye in the backward prolonged ray passing through the point of intersection of the eye. For the perceiving subject this _problem_ does not exist, as the light-sensations of the retinal spots are connected from the beginning with determinate space-sensations. The entire theory of the psychological origin of the “external” world by the projection of sensations outwards is founded in my opinion on a mistaken transference of a _physically_ formulated inquiry into the province of _psychology_. Our sensations of sight and touch are bound up with, are connected with, various _different_ sensations of space, that is to say these sensations have an existence _by the side of_ one another or _outside of_ one another, exist in other words in a _spatial_ field, in which our body fills but a part. That table is thus self-evidently _outside of_ my body. A projection-problem does not present itself, is neither consciously nor unconsciously solved. A physicist (Mariotte) makes the discovery that a certain spot on the retina is blind. He is accustomed to associating with every spatial point an imaged point, and with every imaged point a sensation. Hence the question arises, what do we see at the points that correspond to the blind spots, and how is the gap in the image filled out? If the unfounded influence of the physicist’s method of procedure on the discussion of psychological questions be excluded, it will be found that no problem exists at all here. We see _nothing_ at the blind spots, the gap in the image is _not_ filled out. The gap, moreover, is not felt, for the reason that a defect of light-sensation at a spot blind from the beginning can no more be perceived as a gap in the image than the blindness say of the skin of the back can be so perceived. I have chosen intentionally simple and obvious examples, such as render it clear what unnecessary confusion is caused by the careless transference of a conception or mode of thought which is valid and serviceable in one domain, into another.