Suppose  I  am  looking  at  a  pane  in  a  second-story  window
of  a  distant  house :  its  image  will  then  fall  on  the  fovea  cen-
tralis ;  the  line  joining  this  with  the  pane  is  called  the  visual
axis.  The  image  of  the  roof  will  be  formed  on  a  part  of  the-
retina  below  the  fovea,  and  that  of  the  front  door  above  it.  I
distinguish  that  the  images  of  all  these  fall  on  different  partss
of  the  retina  in  certain  relative  positions,  and  have  learnt,  by
the  experience  of  all  my  life,  that  when  the  image  qf  any--
thing  arouses  the  sensation  due  to  excitation  of'  part  of  the-
retina  below  the  fovea  the  object  is  above  my  visual  axis,  andl
vice  versa  j  similarly  with  right  and  left.  Consequently  I  in-
terpret the  stimulation  of  lower  retinal  regions  as  meaning
high  objects,  and  of  right  retinal  regions  as  meaning  left  ob-
jects, and  never  get  confused  by  the  inverted  retinal  image
about  which  directly  I  know  nothing.  A  new-born  child,
even  supposing  it  could  use  its  muscles  perfectly,  could  not,
except  by  mere  chance,  reach  towards  an  object  which  it  saw ;
it  would  grasp  at  random,  not  yet  having  learnt  that  to  reach
an  object  exciting  a  part  of  the  retina  above  the  fovea  needed
movement  of  the  hand  towards  a  position  in  space  below  the
visual  axis  ;  but  very  soon  it  learns  that  things  near  its  brow,
that  is  vp,  excite  certain  visual  sensations,  and  objects  below
its  eyes  others,  and  similarly  with  regard  to  right  and  left ;  in
time  it  learns  to  interpret  retinal  stimuli  so  as  to  localize
accurately  the  direction,  with  reference  to  its  eyes,  of  outer
objects,  and  never  thenceforth  gets  puzzled  by  retinal  inver-
sion.
