Now in the case of an observation on the mental plane this personal equation would not appreciably affect the impressions received, for since each would thoroughly grasp the entire subject it would be impossible for him to see its parts out of due proportion; but, except in the case of carefully trained and experienced persons, this factor does come into play in transferring the impressions to the lower planes. It is in the nature of things impossible that any account given down here of a vision or experience on the mental plane can be complete, since nine-tenths of what is seen and felt there could not be expressed by physical words at all; and, since all expression must therefore be partial, there is obviously some possibility of selection as to the part expressed. It is for this reason that in all our Theosophical investigations of recent years so much stress has been laid upon the constant checking and verifying of clairvoyant testimony, nothing which rests upon the vision of one person only having been allowed to appear in our later books. But even when the possibility of error from this factor of personal equation has been reduced to a minimum by a careful system of counter-checking, there still remains the very serious difficulty which is inherent in the operation of bringing down impressions from a higher plane to a lower one. This is something analogous to the difficulty experienced by a painter in his endeavour to reproduce a three-dimensional landscape on a flat surface--that is, practically in two dimensions. Just as the artist needs long and careful training of eye and hand before he can produce a satisfactory representation of nature, so does the clairvoyant need long and careful training before he can describe accurately on a lower plane what he sees on a higher one; and the probability of getting an exact description from an untrained person is about equal to that of getting a perfectly-finished landscape from one who has never learnt how to draw. It must be remembered, too, that the most perfect picture is in reality infinitely far from being a reproduction of the scene which it represents, for hardly a single line or angle in it can ever be the same as those in the object copied. It is simply a very ingenious attempt to make upon one only of our five senses, by means of lines and colours on a flat surface, an impression similar to that which would have been made if we had actually had before us the scene depicted. Except by a suggestion dependent entirely on our own previous experience, it can convey to us nothing of the roar of the sea, of the scent of the flowers, of the taste of the fruit, or of the softness or hardness of the surface drawn.