ABSTRACT
All mental training must begin with the development of the senses, by which alone material can come into the mind. The eye and the ear are the chief avenues concerned in the ordinary way, and nine out of ten of the sensations which come into the mind are visual. But our senses actually put us in touch with an extraordinarily small range of vibration. The range of vibrations that the ear can receive, for instance, is approximately from forty a second to about forty thousand. Between this range and that of sight there is an extraordinary gap in which only heat radiations can affect us. Sight begins at about four hundred billion and extends to seven hundred billion vibrations per second, being rather less than the octave. But of radiant waves there are two further octaves beyond the visible violet, and some five others below the visible red. Therefore, although our senses seem to inform us of the world of vibration outside, they tell us, as a matter of fact, of only at best some ten octaves of sound and less than an octave of sight.
