Note 247 — Chapter XX · (continued 3)

The strongest passage in Helmholtz's argument against sensations of space is relative to these fluctuations of seen relief: "Ought one not to conclude that if sensations of relief exist at all, they must be so faint and vague as to have no influence compared with that of past experience? Ought we not to believe that the perception of the third dimension may have arisen without them, since we now see it taking place as well against them as with them?" (Physiol. Optik, p. 817.)