Light by which your eyes see--sound by which your ears hear--are different forms of motion by which you are impressed; odours, flavours, &c., are emanations which strike upon your olfactory nerve or touch your palate; these are solely vibratory motions which are transmitted to your brain. You can only appreciate a few of these movements through the senses you possess, principally those of sight and hearing. You, in your simplicity, believe that you see and hear nature? Nothing of the kind. All you do is to receive some of the movements in activity upon your sublunary atom. That is all. Beyond the impressions you receive there are an infinitely greater number unperceived by you. QUÆRENS. Pardon, master, but this new aspect of nature is not sufficiently clear for me to understand it. Would you.... [Sidenote: The extent of the gamut _re_ vibrations of sound.] [Sidenote: The extent of the vibrations of light.] LUMEN. This aspect is indeed new to you, but attentive reflection will enable you to grasp it. Sound is formed by vibrations in the air which strike upon the membrane of the tympanum and give you the impression of various tones. Man does not hear all sounds. When the vibrations are too slow (below forty a second), the sound is too low; your ear cannot catch it. When the vibrations are too rapid (above 36,000 a second), the sound is too sharp; your ear cannot receive it. Above and below these two limits, therefore, human beings do not perceive them. These vibrations exist, however, and are perceived by creatures of other kinds, as, for example, certain insects. The same rules apply to light. The different aspects of light, the shades and colours of objects, are equally due to the vibrations which strike upon the optic nerve and give you the impression of the different degrees of intensity in light. Man does not by any means see all that is visible. When the vibrations are too slow (under 458 billions a second), light is too feeble; your eye sees nothing. When the vibrations are too rapid (over 727 billions a second), light outruns your organic faculty of perception and is invisible to you. Above and below these two limits the vibrations of ether still exist, and are perceived by other beings. You do not know therefore, nor can you receive, any impressions except those that can be made to vibrate upon the two chords of your organic lyre, called respectively the optic nerve and the auditory nerve. Imagine for one instant the extent of all the sights and sounds which are not perceptible to you. All the undulatory movements that exist in the universe between the figures of 36,000 and those represented by 458,000,000,000,000 in the same unity of time, can neither be heard nor be seen by you, and remain utterly unknown to you. [Sidenote: Man deaf to the concert of universal harmonies by reason of his limitations.]