In higher stages of development the process of analytic touch takes a form such as the following. One hand holds the object in position, and turns it so that it may be conveniently explored by the other. Finger and thumb are the instruments of exploration, and they are used simultaneously. The finger glides along one contour of the object, and the thumb along an opposite contour. The varying distance of finger and thumb, as they proceed from their startingpoint, measures and determines the distance and direction of the boundary lines. If finger and thumb retain the same relative position, the boundary lines are parallel; if they move apart, the boundary lines are divergent; if they approach each other, the boundary lines are convergent. Many blind persons have wonderful power of discriminating distance in this way. They can, for example, determine the various thickness of different kinds of paper. When in this process of analytic exploration the object is pushed backwards till it touches the surface of the hand, analytic touch passes into synthetic. The two hands sometimes interchange functions, and at intervals synthetic touch intervenes, the object being clasped and pressed. As a rule, synthetic touch comes first, and introduces analytic. All active exploration is brought into connexion with the total presentation of the object, as it exists for passive touch. The more practised a blind person is in the apprehension of the configuration of bodies, the more rapid and sketchy are the active movements necessary for adequate perception. Indeed, all the facts show that neither active nor passive touch alone suffices. The perception of spatial order is a product of their union and interaction. This cooperation of synthetic and analytic touch is possible only for objects small enough to be taken in the hand, or at least in both hands. Larger objects cannot be apprehended as a whole by synthetic touch. Active movement, it would seem, must in these cases be the main resource. But this is not quite true. The blind person can often measure the dimensions of the object by the dimensions of his own body, comparing, for instance, its height with his own height.*

* We shall presently have to consider the conditions under which the spatial relations of the body itself come to be presented.

The significance of analytic touch as applied to larger objects depends upon the significance which it has acquired in cooperation with synthetic touch. Large numbers of blind persons are unable to acquire precise spatial apprehension of those objects which cannot be immediately clasped by the hand. This inability manifests itself in their movements of active touch, which are for the most part limited to the discovery of some striking and distinctive feature of the object which can serve as a sign of it. But it is often possible to induce these persons to undertake a systematic exploration of larger objects in the way of active movement, by putting before them models of these objects on a reduced scale. They are thus prompted to compare originals and copies. Afterwards they freely apply the system of movements thus acquired to all objects which require and admit of them. As in the active exploration of small objects the convergence and divergence of thumb and finger play a prominent part, so in the exploration of larger objects, the convergence and divergence of the two arms is of the greatest value. There is a link of connexion between these two methods, inasmuch as it is possible to use either of the two methods for smaller objects. A thing may either be taken between the opposing thumb and fingertip or between the opposing fingers of the two hands.

So far, we have dealt with the exploration of comparatively limited spaces. We have kept within what may be called the touch horizon. This is very much more restricted than the visual horizon. Its utmost limit is the space that can be embraced by the outstretched arms. Larger spaces than these can only be explored by locomotion of the whole body, in which extension previously presented is completely left behind. We thus have a series of fragmentary presentations. For fully precise spatial apprehension these must be gathered together into a single simultaneously presented whole. It is conceivable that this might be effected by ideal reproduction of the parts not immediately perceived. To a certain extent the blind may actually proceed in this way. But they can only do so by reproducing the whole on a reduced scale. The scale of their imagination is limited by the range of their actual perception. The same is true of those who can see. We cannot mentally visualise a spatial expanse larger than the field of view as given in actual perception.* If we are to include in the purely mental field of view objects beyond the range of actual vision, we must make a schematic representation of them on a reduced scale. Those who are confined to the sense of touch may follow an analogous plan; but their power in this respect varies with the individual, and is in any case very much more restricted than that of persons who can see. But we must not suppose that where the apprehension of the parts of a spatial whole becomes purely successive, the parts themselves are presented as successive, so as to transform a spatial perception into a temporal perception. On the contrary the movements of exploration have already acquired a spatial significance through the experiences obtained within the limits of the touch horizon. Hence the parts of the spatial whole which successively present themselves are apprehended as related in the way of coexistence, although they cannot be simultaneously presented. Similarly, a person who can see, in walking along a road for ten miles, has a number of successive fields of view which cannot be simultaneously presented either actually or ideally. But he does not apprehend these fields of view as forming a time series: he apprehends them as successively presented parts of a coexistent whole. The reason for this will become clearer in the next section.

* Of course we can think of such an expanse, although we cannot picture it.