This experiment was repeated several times, with four subjects, and with both clockwise and anti-clockwise rotations, and the results were uniformly as described above. In order to see whether this motion of the after-image really depended on the slower nystagmiform movements, the following variation was tried. It will be recalled that if the head is rotated not about a vertical (longitudinal) axis, but about a transverse axis, as, say, one passing through the ears, a nystagmus is produced in which during the rotation the slower eye-movements are opposite to the direction of rotation, while when the rotation is checked or stopped, the nystagmus, as before, reverses. The same is true if the rotation is about a sagittal axis. These conditions were approximately realized by having the subject sit as before on the rotary chair, but during the rotation hold his head horizontally to the right or left, forward or back. With any of these positions of the head, however, the rotation produced, on all of the subjects tried, extreme dizziness and a feeling of nausea that lasted in some cases for several hours. This fact made it impossible to ask for a set of the four possible positions of the head from any of the subjects. The following are the records that were obtained: Subject Fl. Head horizontally to left; rot. anti-clockwise. During rot.; after-im. moved clockwise, _i. e._, from subject's brow to chin. Eye-mov. not observable during rot. After rot.; after-im. moved anti-clockwise, chin to brow. Slow eye-mov. anti-clockwise, chin to brow. Vis. field clockwise, brow to chin. Subject H. Head horizontally to right; rot. anti-clockwise. During rot.; after-im. clockwise, chin to brow. Eye-mov. not observable. After rot.; after-im. anti-clockwise, brow to chin. Slow eye-mov. anti-clockwise, brow to chin. Vis. field clockwise, chin to brow. Subject H. Same repeated, with same results. Subject H. Same as case of Fl., with identical results. Subject K. Head horizontally to left; rot. anti-clockwise. During rot.; after-im. not observed. After rot.; after-im. anti-clockwise, chin to brow. Slow eye-mov. anti-clockwise, chin to brow. Vis. field not observed.