In the investigation of the phenomena of clairvoyance all these varied types and many others will be encountered, and a certain number of cases of mere hallucination will be almost sure to appear also, and will have to be carefully weeded out from the list of examples. The student of such a subject needs an inexhaustible fund of patience and steady perseverance, but if he goes on long enough he will begin dimly to discern order behind the chaos, and will gradually get some idea of the great laws under which the whole evolution is working. It will help him greatly in his efforts if he will adopt the order which we have just followed--that is, if he will first take the trouble to familiarize himself as thoroughly as may be with the actual facts concerning the planes with which ordinary clairvoyance deals. If he will learn what there really is to be seen with astral and etheric sight, and what their respective limitations are, he will then have, as it were, a standard by which to measure the cases which he observes. Since all instances of partial sight must of necessity fit into some niche in this whole, if he has the outline of the entire scheme in his head he will find it comparatively easy with a little practice to classify the instances with which he is called upon to deal. We have said nothing as yet as to the still more wonderful possibilities of clairvoyance upon the mental plane, nor indeed is it necessary that much should be said, as it is exceedingly improbable that the investigator will ever meet with any examples of it except among pupils properly trained in some of the very highest schools of occultism. For them it opens up yet another new world, vaster far than all those beneath it--a world in which all that we can imagine of utmost glory and splendour is the commonplace of existence. Some account of its marvellous faculty, its eneffable bliss, its magnificent opportunities for learning and for work, is given in the sixth of our Theosophical manuals, and to that the student may be referred. All that it has to give--all of it at least that he can assimilate--is within the reach of the trained pupil, but for the untrained clairvoyant to touch it is hardly more than a bare possibility. It has been done in mesmeric trance, but the occurrence is of exceeding rarity, for it needs almost superhuman qualifications in the way of lofty spiritual aspiration and absolute purity of thought and intention upon the part both of the subject and the operator. To a type of clairvoyance such as this, and still more fully to that which belongs to the plane next above it, the name of spiritual sight may reasonably be applied; and since the celestial world to which it opens our eyes lies all round us here and now, it is fit that our passing reference to it should be made under the heading of simple clairvoyance, though it may be necessary to allude to it again when dealing with clairvoyance in space, to which we will now pass on. CHAPTER IV.