I. 
The  Methods  and  the  Material. 
Our  knowledge  of  the  ocean-currents  is,  as  iS  well  known,  based 
to  a great  extent  on  conclusions  drawn  from  the  distribution  of 
salinity  and  temperature.  The  knowledge  obtained  in  this  way  is 
rather  superficial  and  has  reference  only  to  the  direction  of  the 
drift  of  large  masses  of  water.  Calculations  made  as  to  the  ve lo- 
cities  of  currents  still  rest  upon  an  insecure  foundation  and  the 
inner  mechanism  of  the  movements  cannot  be  followed  at  all.  In 
order  to  obtain  more  complete  information  it  will  be  necessary  to 
observe  the  velocities  at  a large  number  of  localities  and  under 
varying  conditions,  noting  at  the  same  time  the  distribution  of  pres- 
sure  and  density  and  the  wind-conditions  as  well. 
It  was  only  the  strengest  ocean-currents  that,  till  a few  years 
ago,  had  been  determined  by  direct  methods.  Deviations  in  reckonings 
have  mostly  been  used  for  determining  the  surface  movements  directly. 
However  it  is  obvious  that  the  method  is  of  little  accuracy  or  of 
none  at  all  if  the  strength  of  the  current  do  not  exceed  some  20 
centimeters  per  secoud.  Compared  with  the  records  thus  collected, 
the  measurements  made  from  a fixed  point  with  a stream-gauge  will 
not  appear  many.  They  have  with  some  few  exceptions  been  only 
carried  out  in  shallow  water  along  the  coast,  generally  from  light- 
ships.  Still  they  give  valuable  material  for  estimating  the  currents 
along  the  coasts.  The  Americans  as  early  as  1885  ascertained  by 
an  indefatigable  series  of  measurements  the  velocity  of  the  Gulf 
Stream  in  the  Strait  of  Florida.  But  in  the  open  sea  no  reliable 
direct  measurements  have  been  made  until  the  year  1901,  as  far  as 
I know.  What  we  have  ascertained  about  currents  by  means  of  drift- 
bottles  is  absolutely  unreliable,  and  no  real  knowledge  has  been 
