It may help to dispel this sense of unreality if we try to understand that clairvoyance, like so many other things in nature, is mainly a question of vibrations, and is in fact nothing but an extension of powers which we are all using every day of our lives. We are living all the while surrounded by a vast sea of mingled air and ether, the latter inter-penetrating the former, as it does all physical matter; and it is chiefly by means of vibrations in that vast sea of matter that impressions reach us from the outside. This much we all know, but it may perhaps never have occurred to many of us that the number of these vibrations to which we are capable of responding is in reality quite infinitesimal. Up among the exceedingly rapid vibrations which affect the ether there is a certain small section--a _very_ small section--to which the retina of the human eye is capable of responding, and these particular vibrations produce in us the sensation which we call light. That is to say, we are capable of seeing only those objects from which light of that particular kind can either issue or be reflected. In exactly the same way the tympanum of the human ear is capable of responding to a certain very small range of comparatively slow vibrations--slow enough to affect the air which surrounds us; and so the only sounds which we can hear are those made by objects which are able to vibrate at some rate within that particular range. In both cases it is a matter perfectly well known to science that there are large numbers of vibrations both above and below these two sections, and that consequently there is much light that we cannot see, and there are many sounds to which our ears are deaf. In the case of light the action of these higher and lower vibrations is easily perceptible in the effects produced by the actinic rays at one end of the spectrum and the heat rays at the other. As a matter of fact there exist vibrations of every conceivable degree of rapidity, filling the whole vast space intervening between the slow sound waves and the swift light waves; nor is even that all, for there are undoubtedly vibrations slower than those of sound, and a whole infinity of them which are swifter than those known to us as light. So we begin to understand that the vibrations by which we see and hear are only like two tiny groups of a few strings selected from an enormous harp of practically infinite extent, and when we think how much we have been able to learn and infer from the use of those minute fragments, we see vaguely what possibilities might lie before us if we were enabled to utilize the vast and wonderful whole.