The observer resuming the position in the figure where his eyes, L, R, are _twelve_ inches distant from MN, let us consider the important results of this experiment. If he now grasps the cane bottom at MN, his thumbs pressing upon MN, and his fingers trying to grasp _mn_, he will then _feel what he does not see_, and _see what he does not feel_! The real pattern is absolutely invisible at MN, where he feels it, and it stands fixed at _mn_. The fingers may be passed through and through between the real and the false image, and beyond it,—now seen on this side of it, now in the middle of it, and now on the other side of it. If we next place the palms of each hand upon MN, the real bottom of the chair, feeling it all over, the result will be the same. No knowledge derived from touch—no measurement of real distance—no actual demonstration from previous or subsequent vision, that there is a real solid body at MN, and nothing at all at _mn_, will remove or shake the infallible conviction of the sense of sight that the cane bottom is at _mn_, and that _d_L or _d_R is its real distance from the observer. If the binocular centre be now drawn back to MN, the image _seen_ at _mn_ will disappear, and the real object be _seen and felt at_ MN. If the binocular centre be brought further back to _f_, that is, if the optic axes are converged to a point nearer the observer than the object, as illustrated by Fig. 18, the cane bottom MN will again disappear, and will be seen at _uv_, as previously explained. This method of uniting small similar figures is more easily attained than that of doing it by converging the axes to a point between the eye and the object. It puts a very little strain upon the eyes, as we cannot thus unite figures the distance of whose centre is equal to or exceeds 2½ inches, as appears from Fig. 22. In making these experiments, the observer cannot fail to be struck with the remarkable fact, that though the openings MN, _mn_, _uv_, have all the same apparent or angular magnitude, that is, subtend the same angle at the eye, viz., _d_L_c_, _d_R_e_, yet those at _mn_ appear larger, and those at _uv_ smaller, than those at MN. If we cause the image _mn_ to recede and approach to us, the figures in _mn_ will invariably _increase as they recede_, and those in _uv_ diminish as they approach the eye, and their _visual magnitudes_, as we may call them, will depend on the respective distances at which the observer, whether right or wrong in his estimate, conceives them to be placed,—a result which is finely illustrated by the different size of the moon when seen in the horizon and in the meridian. The fact now stated is a general one, which the preceding experiments demonstrate; and though our estimate of magnitude thus formed is erroneous, yet it is one which neither reason nor experience is able to correct.