deep-lying common origin in the motor sensations. My experiments show
that, even in the highly differentiated form in which we find them in
their ordinary functioning, they plainly reveal their common origin. A
formula, then, for expressing the judgments of distance by means of
the resting skin might be put in this way. Let _P_ and _P'_ represent
any two points on the skin, and let _L_ and _L'_ represent the local
signs of these points, and _M_ and _M'_ the muscle sensations which
give rise to these local signs. Then _M-M'_ will represent the
distance between _P_ and _P'_, whether that distance be judged
directly in terms of the localizing function of the skin or in terms
of its space-perceiving function. This would be the formula for a
normal judgment. In an illusory judgment, the temporal and æsthetic
factors enter as disturbing elements. Now, the point which I insist on
here is that the judgments of the extent of the voluntary movements,
represented in the formula by _M_ and _M'_, do not depend alone on the
sensations from the moving parts or other sensations of objective
origin, as Dresslar would say, nor alone on the intention or impulse
or innervation as Loeb and others claim, but on the sum of all the
sensory elements that enter, both those of external and those of
internal origin. And, furthermore, these sensations of external origin
are important in judgments of space, only in so far as they are
referred to sensations of internal origin. Delabarre says, "Movements
are judged equal when their sensory elements are judged equal. These
sensory elements need not all have their source in the moving parts.
All sensations which are added from other parts of the body and which
are not recognized as coming from these distant sources, are mingled
with the elements from the moving member, and influence the
judgment."[18] The importance of these sensations of inner origin was
shown in many of the experiments in sections VI. to VIII. In the
instance where the finger-tip was drawn over an open and a filled