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 206 w. JAMES : limb is there l as when it is not. Extradition obtains, then, even of such sensations as we locate on the exact sensory surfaces where the nerves terminate. Could we feel our retinal pictures where they are, this would involve a dealing with the third dimension quite as thorough as does our feel- ing them across the room. The distinction so often made between our primitive spatial perception as that of a surface, and our perception of the third dimension as subsequent and acquired, is utterly baseless. For to feel any surface, as such, involves all three dimensions. The only difference between primitive and acquired in this department of consciousness is the difference between vague and unbroken on the one hand, and subdivided and measured on the other. It is conceivable that the subdivi- sion of either dimension might be earlier and more accurate than that of the two others, but it is inconceivable that either dimension should appear out of relation to the others, incon- ceivable that the very earliest apprehension of space should not be that of space cubic, as it really exists. Those philo- sophers therefore who hold that the prim of all external per- ception is the vague consciousness of the body as cubically extended must be held to be essentially in the right. 2 To return now, after this theoretic digression, to our spe- cial facts. For a joint to be felt in situ, the entire intervening mass of tissue between it and the brain must be susceptible of becom- ing one continuous object of perception. The existence of thi& intervening space-object is the conditio sine qua non of the joint's ' projection ' to the farther end of it. To say nothing of other ways in which this space may be felt (as by the eye or the exploring hand), it is felt by means of its own nerves, whose local-signs pass gradually into those in and about the joint, and give us, whenever they awaken together, a unitary massive space. For the finger-tip to be felt where 1 In a purely subjective account, its ' being ; there means, i only the presence of other feelings than the one in question, 'there 3 iust as it is. of course, projected
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2 Of late years the doctrine has been revived by I. H. Fichte and Ulrici that the soul itself is a cubically extended substance pervading the body, and that the latter becomes the " immediate object " in perception through the fact that the perceiving subject is coextensive with it. And this view has been defended in a recent American work of unusual critical ability - The Perception of Space and Matter, by J. E. Walter, Boston, 1880. (Cp. Noah Porter's Human Intellect, p. 130.) But it is not necessary that we should commit ourselves either to the theory of an extended soul-substance or to that of the body as "immediate object". I only cite these theories to illustrate the need which coerces men to postulate something tridimen- sional as the first thing in external perception.