Idltlo  as  wo  habitually  obwcrvc  it,  it  in  yet  certain  that  tho
impulses  our  actions  impress  &om  toomont  to  moment  on
Burrounding  objects,  aro  propogated  through  tbem  in  vibra-
tions. It  ni<cd«  but  to  look  through  a  ti^lowopo  of  high
powor,  to  bo  conrineed  that  each  pulsation  of  tbe  b«ui  givea
n  jar  to  tho  whole  room.  If  we  pcuts  to  motioms  of

another  order— those  namely  which  take  place  in  the  elhertul
medium — wo  still  find  tlio  same  thing.  Brery  fresh  dis-
ooreiy  confirms  the  hypothesis  that  li^ht  consists  of  trndnla-
tJoDs.  Tho  mys  of  heut,  loo,  are  now  found  to  havo  a  liko
fundamental  miture  :  their  ondulalions  differing  from  those
of  light  only  in  their  comparaCiTc  lengths.  Kor  do  the  morc-
menta  of  eloctncily  fail  to  fiimiiOi  va  vrilh  an  illustration ;
though  one  of  a  dilTerent  order.  Tbe  northern  aurora  majr
often  bo  obeerred  to  pulsate  with  wavos  of  greater  brightnon ;
and  tlic  electric  diwhnrp;  tlirintgb  a  vacuum  shows  ui  by  ita
etratified  appearance  that  the  current  is  not  uniform,  but
oomca  in  gushes  of  gnittcr  oiid  leesor  intensity.  Should

it  be  said  that  at  any  rate  there  are  some  motions,  as  those  of
projoctiles,  which  aro  not  rhjthmical,  the  reply  is,  lliat  tlwj
exception  is  appurcnt  only ;  and  that  these  motions  would  bo
rhytJiinicftl  if  they  were  not  intcrrui>Uil.  It  is  common  to
assert  that  the  trajectory  of  a  cannon  bull  la  a  parabola ;  and
it  is  true  that  (omitting  atmospheric  resistance)  tho  curre  dc-
iwribod  diifors  so  slightly  from  a  parabola  that  it  may  prooti-
coUy  be  regarded  as  one.  But,  strictly  speaking,  it  is  a  por-
tion of  an  extremely  cceentric  ellipse,  having  the  Kurtk's
centre  of  gravity  for  its  remoter  focus  ;  and  but  for  its  arrest
by  tho  substance  of  the  Earth,  tho  cannon  hall  would  tniTet


TIIR   RltTTHM  Of  UOTIIMr.
