But, it may be said, the mere fact that he is using astral sight ought to enable him to see it from all sides at once. So it would if he were using that sight in the normal way upon an object which was fairly near him--within his astral reach, as it were; but at a distance of hundreds or thousands of miles the case is very different. Astral sight gives us the advantage of an additional dimension, but there is still such a thing as position in that dimension, and it is naturally a potent factor in limiting the use of the powers of its plane. Our ordinary three-dimensional sight enables us to see at once every point of the interior of a two-dimensional figure, such as a square, but in order to do that the square must be within a reasonable distance from our eyes; the mere additional dimension will avail a man in London but little in his endeavour to examine a square in Calcutta. Astral sight, when it is cramped by being directed along what is practically a tube, is limited very much as physical sight would be under similar circumstances; though if possessed in perfection it will still continue to show, even at that distance, the auras, and therefore all the emotions and most of the thoughts of the people under observation. There are many people for whom this type of clairvoyance is very much facilitated if they have at hand some physical object which can be used as a starting-point for their astral tube--a convenient focus for their will-power. A ball of crystal is the commonest and most effectual of such foci, since it has the additional advantage of possessing within itself qualities which stimulate psychic faculty; but other objects are also employed, to which we shall find it necessary to refer more particularly when we come to consider semi-intentional clairvoyance. In connection with this astral-current form of clairvoyance, as with others, we find that there are some psychics who are unable to use it except when under the influence of mesmerism. The peculiarity in this case is that among such psychics there are two varieties--one in which by being thus set free the man is enabled to make a telescope for himself, and another in which the magnetizer himself makes the telescope and the subject is simply enabled to see through it. In this latter case obviously the subject has not enough will to form a tube for himself, and the operator, though possessed of the necessary will-power, is not clairvoyant, or he could see through his own tube without needing help.