t period of the anaesthesia, as observed in the
experiments. It is true that this latent period was observed only in
long eye-and head-movements, but the experiments were not delicate
enough in this particular to bring out the finer points.

Finally, the conditioning of anaesthesia by movements of the head, if
really proved, would rather corroborate this interpretation. For of
course the position of the head on the shoulders is as important for
localization of the retinal picture as the position of the eyes in the
head, so that sensations of head-movements must be equally represented
in the localization centers; and head movements would equally raise
the tension on those centers against discharge-currents from the
color-centers.

The conclusion from the foregoing experiments is that voluntary
movements of the eyes condition a momentary, visual, central
anaesthesia.

* * * * *

TACTUAL ILLUSIONS.

BY CHARLES H. RIEBER.

I.

Many profound researches have been published upon the subject of
optical illusions, but in the field of tactual illusions no equally
extensive and serious work has been accomplished. The reason for this
apparent neglect of the illusions of touch is obviously the fact that
the studies in the optical illusions are generally thought to yield
more important results for psychology than corresponding studies in
the field of touch. Then, too, the optical studies are more attractive
by reason of the comparative ease and certainty with which the
statistics are gathered there. An optical illusion is discovered in a
single instance of the phenomenon. We are aware of the illusion almost
immediately. But in the case of most of the illusions of touch, a
large number of experiments is often necessary in order to reveal any
approximately constant error in the judgments. Nevertheless, it seems
to me that the factors that influence our judgments of visual space,
though their effects are nearly always immediately apparent, are of no
more vital significance for the final explanation of the origin of our
notion of space than the disturbing factors in our estimations of
tactual space whose effects are not so open to direct observation.

The present investigation has for its main object a critical
examination of the tactual illusions that correspond to some of the
well-known optical illusions, in the hope of segregating some of the
various disturbing factors that enter int