1907] 
Carrent-Measui’ements. 
29 
(5)  Coneluding  remarks. 
The  observations  dealt  with  in  the  preceding-  pages  will  prove, 
I hope,  that  it  is  now  possible  to  obtain  reliable  observations  of  the 
dynamical  phenomena  of  the  sea,  even  where  the  depth  is  consider- 
able.  Our  stations  belong  to  different  groups  as  far  as  currents 
are  eoncerned : some  of  them  are  situated  in  areas,  where  the  regnlar 
tidal  currents  completely  predominate,  as  for  instance  St.  332  on 
the  Ling  Bank; — others  in  areas,  where  the  tidal  currents  are  of 
very  little  importance  indeed  compared  to  the  other  movements,  e.  g. 
the  upper  layers  at  the  stations  in  the  Skagerack.  The  variations 
found  in  the  Norwegian  Sea  (St.  307,  at  the  Edge)  do  not  exhibit 
the  regular  semi-diurnal  type  of  tide ; it  is  difficult  to  decide,  whether 
these  variations  are  due  to  a diurnal  period  of  the  tides,  or  whether 
they  have  no  connexion  with  the  tidal  phenomena  at  all.  Between 
the  two  groups  mentioned  several  transition-forms  are  to  be  found, 
e.  g.  St.  299  off  Sondinore  and  St.  312  in  the  Norse  Rent. 
The  different  movements  may  be  systematised,  and  the  various  in- 
fluences  eliminated  by  analysis.  Even  in  areas  where  the  resulting 
current  is  only  slightly  perceptible,  it  is  still  possible  to  trace  it 
and  to  follow  the  general  drift  of  the  whole  body  of  water.  It  is 
also  a vey  interesting  fact,  that  the  tidal  currents  in  the  deeper 
water-layers  can  be  defined,  even  where  they  are  weak:  as  we  were 
surprised  to  discover  was  the  case  at  stations  318  a and  324  in  the 
Skagerack. 
Our  studies  of  the  tides  will  obviously  be  very  much  assisted 
by  extensive  observations  of  this  kind.  Charts  of  co-tidal  lines  will 
then — as  I have  tried  to  point  out  above— be  certainly  much  im- 
proved,  aud  the  progress  of  the  tidal  wave  will  be  exactly  traced. 
The  North  Sea  offers  a most  interesting  field  of  observation  in  this 
respect. — 
In  most  cases  the  direction  as  well  as  the  strength  of  the  cur- 
rents alters  at  very  short  periods,  and  a single  observation  at  a 
given  moment  is  not  likely  to  afford  a clear  idea  of  their  mean 
velocity  and  direction.  We  know  too  little  about  tfiem  to  be  able 
to  tell  how  mauy  observations  are  necessary  determine  them  properly. 
A general  study  of  these  movements  of  vortices  aud  kindred  phenomena 
is  in  the  highest  degree  desirable.  It  does  not  seem  too  sanguine 
