A little attention will show that this sense of effort accompanies every muscular contraction by which the limbs, or other parts of the body, are moved.  By its agency the fact of their movement is known; while the direction of the motion is given by the accompanying tactile sensations.  And, in consequence of the incessant association of the muscular and the tactile sensations, they become so fused together that they are often confounded tinder the same name.

If freedom to move in all directions is the very essence of that conception of space of three dimensions which we obtain by the sense of touch; and if that freedom to move is really another name for the feeling of unopposed effort, accompanied by that of change of place, it is surely impossible to conceive of such space as having existence apart from that which is conscious of effort.

But it may be said that we derive our conception of space of three dimensions not only from touch, but from vision; that if we do not feel things actually outside us, at any rate we see them.  And it was exactly this difficulty which presented itself to Berkeley at the outset of his speculations.  He met it, with characteristic boldness, by denying that we do see things outside us; and, with no less characteristic ingenuity, by devising that “New Theory of Vision” which has met with wider acceptance than any of his views, though it has been the subject of continual controversies.[1]

[Footnote 1:  I have not specifically alluded to the writings of Bailey, Mill, Abbott, and others, on this vexed question, not because I have failed to study them carefully, but because this is not a convenient occasion for controversial discussion.  Those who are acquainted with the subject, however, will observe that the view I have taken agrees substantially with that of Mr. Barley.]

In the “Principles of Human Knowledge,” Berkeley himself tells us how he was led to those views which he published in the “Essay towards the New Theory of Vision.”

“It will be objected that we see things actually without, or at a distance from us, and which consequently do not exist in the mind; it being absurd that those things which are seen at the distance of several miles, should be as near to us as our own thoughts.  In answer to this, I desire it may be considered that in a dream we do oft perceive things as existing at a great distance off, and yet, for all that, those things are acknowledged to have their existence only in the mind.

“But for the fuller clearing of this point, it may be worth while to consider how it is that we perceive distance and things placed at a distance by sight.  For that we should in truth see external space and bodies actually existing in it, some nearer, others further off, seems to carry with it some opposition to what hath been said of their existing nowhere without the mind.  The consideration of this difficulty it was that gave birth to my ’Essay towards