Kepler, Johannes - Harmonices Mundi Libri V
Type of Spiritual Experience
A description of the experience
Johannes Kepler – Harmonices Mundi Libri V 1619
When the tension of two strings is the same, so that they sound in unison, then the sound of one, i.e. the immaterial species of the body of the string caused by the vibration, leaves its own string and moves the other one. It is the same when one shouts near a lute or any other hollow body; the shout shakes the cavity and makes all its strings vibrate.
This species of vibration moves the second string in the same rhythm of speed as the latter would move in, because it is tuned alike, in the following way. The single impulses (into which we must understand that a vibration is divided) arouse in the other struck string single rebounds. Thus the string that will be moved most of all is the one which is tuned in unison to the first; but the string of double or half speed will also be moved, because two impulses of vibration will be resolved in one rebound of the string and thus every third impulse will coincide with the end of a rebound. Finally the string will not remain unmoved when the speeds are 3:2 for then the three impulses and those rebounds begin to interfere with and impede each other more frequently since two impulses are contrary to the end of a rebound while only one coincides.
When this happens, the motion of the other strings is stopped just as if one had touched a finger to the vibrating one. This seems to me to be the cause of this remarkable experiment, but I will give the palm to anyone who is better endowed with mental penetration than myself