Physical  analysis  of  sound,  using  this  term  in  its  exact
significance  of  auditory  sensations,  has  shown  that  the  ulti-
mate sound  unit  is  the  result  of  isochronous  vibrations  of
matter,  manifesting  but  three  phenomena,  each  of  which
produces  a  characteristic  sensory  impression.  These  ma-
terial vibratory  phenomena  and  their  sensory  indications,
known  as  the  elements  of  sound,  are:  1.  Rapidity  of
vibrations,  determining  pitch.  2.  Amplitude  or  extent
of  vibrations,  fixing  initial  intensity  or  loudness.  3.  Con-
tinuance, the  primary  cause  of  length  of  sound.
While  this  ultimate  sound  unit  of  physics,  caused  by  a
single  set  of  vibrations  with  three  inseparable  phenom-
ena, and  therefore  presenting  only  the  elements  of  pitch,
intensity,  and  duration,  must  never  be  lost  sight  of  as  the
basis  of  all  sounds,  it  is  equally  important  to  remember
that  the  unit  of  applied  acoustics  is  determined  solely  by
the  ear,  and  that  this  unit,  even  with  the  maximum  limit
of  auditory  acumen,  is,  of  necessity,  a  complex  product,
since  the  relations  and  properties  of  matter  render  the  de-
velopment of  multiple  sets  of  sonorous  vibrations  an  in-
evitable accompaniment  of  the  excitation  of  one  such  set.
The  physical  demonstration,  by  which  all  auditory  im-
pressions are  shown  to  be  multiple,  discloses  limitations
to  our  powers  of  auditory  analysis  that  instantly  assume
a  position  of  fundamental  importance,  as  determining  the


1 1 6  QUIMBY :    The  Applied  Physics

sole  clinical  standard  for  estimating  the  composition  and
elements  of  sound.
It  will  be  useless  for  anyone  to  read  further  who  does
not  clearly  recognize  the  significance  of  this  relation  as
the  point  of  contact  between  pure  and  applied  acoustics,
and  appreciate  that  the  transition  to  the  latter  involves
the  introduction  of  a  variable  personal  factor,  and  its  con-
stant presence  in  every  problem  of  applied  acoustics.
