1907] 
Current-Measurements. 
5 
tlie  steamer.  They  have  found  that  any  direct  connection  between 
sliip  and  apparatus  entails  so  many  jerks  upon  the  latter  that  the 
measurements  are  quite  iintrustworthy.  Many  attempts  have  been 
made  — some  of  them  by  ourselves  — to  see  if  it  were  possible 
to  carry  out  the  measurements  from  a steamer  at  anchor.  A vessel 
can  be  anchored  fore  and  aft  if  the  depths  are  small:  and  provided 
the  velocities  are  considerable,  comparatively  accurate  observations 
can  be  thus  obtained. 
Howevei’  it  is  impossible  to  anchor  a vessel  of  any  size  in  this 
way  when  the  depths  are  great;  and  with  ouly  one  anchor  out 
there  is  generally  such  a drift  that  the  motion  of  the  sliip  itself 
becomes  far  too  perceptible.  No  trustworthy  measurements  of  slight 
currents  at  any  i-ate  could  be  got. 
We  have  for  instance  made  a number  of  trials  in  a liord  where 
the  depth  was  about  50  meters.  The  ,, Michael  Sars“  was  anchored, 
and  through  an  eye  in  the  anchor  a thin  wire  was  carried  to  the 
stream-gauge  which  Avas  kept  tloating  by  means  of  a buoy.  The 
AAmather  Avas  calm  and  the  sea  smooth.  On  sinking  the  gange  to 
a depth  af  5 meters  beloAv  the  surface  it  appeared  that  the  move- 
ment  set  up  betAveen  the  vessel  and  the  anchor  Avas  so  consider- 
able that  the  apparatus  kept  coming  to  the  surface  and  then  sank 
deep  doAvn  again  out  of  sight. 
In  the  mouths  of  May  and  June  1901  Ave  tried  the  experiment 
not  only  in  the  Norse  tiords,  but  also  right  out  in  the  North  Sea 
of  anchoring  a little  bo  at  (the  jollyboat  of  the  „Michael  Sars“) 
Avith  tAvo  grapnels  in  100  meters  of  Avater:  the  hemp  lines  Avere 
tautened  as  much  as  possible,  so  that  the  boat  lay  Avith  a strong 
strain  on  hor  from  both  grapnels.  From  subsequent  experiments 
in  1905  and  1906  Ave  found  that  a little  boat  can  be  anchored  in 
this  manner  even  in  Avater  as  deep  as  500  meters:  though  no  at- 
tempts have  so  far  been  made  to  ascertain  if  it  can  be  done  at 
greater  depths. 
In  the  fiords  one  is  able  to  get  extremely  exact  laudmarks, 
so  that  a drift  of  5 to  10  meters  can  easily  be  perceived.  We 
have  on  several  occasions  found  out  the  distance  Avhich  the  boat 
has  drifted  by  merely  roAving  in  anothor  boat  to  AAdiere  Ave  had 
taken  our  original  bearings:  and  in  spite  of  our  having  made  this 
test  repeatedly,  Ave  have  neAmr  found  the  drift  to  be  of  any  material 
consequence;  even  though  a fairly  strong  AAund  might  be  bloAAung 
doAvn  the  fiord.  (See  further  on,  page  9). 
