582  THE  RISE  AND  EALL  OE  LAKE  TANGANYIKA.  [HoV.  1 893. 
the  oscillations  of  the  lake  as  the  effect  of  climatic  variations  and 
of  the  resulting  changes  in  the  current,  the  depth,  and  the  volume 
of  the  Lukuga.  As  the  climatic  causes  act  periodically,  it  is 
probable  that  the  blocking-up  and  reopening  of  the  Lukuga  are 
similarly  periodical  (although  the  periodicity  is  not  that  of  15  to 
20  years,  advocated  by  Ochsenius,  whose  suggestion  hardly  accords 
with  the  observed  facts). 
It  will  be  a  highly  interesting  study  to  watch  the  future  fate  of 
the  Lukuga,  its  increase  or  decrease  in  volume,  and  the  action  of 
erosion  on  the  river-bed.  It  would,  moreover,  be  a  work  of  really 
considerable  importance  to  connect  a  system  of  regular  observations 
of  water-marks  or  level-gauges  with  meteorological  observations, 
not  only  along  the  shores  of  Lake  Tanganyika,  but  also  along  those 
of  other  African  lakes,  and  so  to  eliminate  the  influences  of  seismic 
and  other  tectonic  agencies,  and  to  determine  with  some  certainty 
the  periodicity  of  meteorological  epochs.  Perhaps  the  period  of 
subsiding  level  is  already  nearing  its  end  in  the  African  lakes — and 
in  that  case  we  may  expect  a  simultaneous  rise  of  Tanganyika  and 
the  Lukuga,  which  would  furnish  a  striking  proof  of  the  correctness 
of  my  opinion  that  the  change  of  level  in  Lake  Tanganyika  is 
rather  a  meteorological  than  a  geological  phenomenon. 
The  subsidence  of  Lake  Tanganyika  was  still  going  on  in  September 
1  892,  as  reported  by  l)r.  Baumann.1  A  recent  decrease  of  its  tribu¬ 
taries  has  been  observed  by  Mr.  Shaw  during  a  residence  of  ten 
}Tears  at  Lrambo,  but  is  regarded  by  Dr.  Baumann  as  a  mere  con¬ 
sequence  of  the  sinking  of  the  lake  itself,  because  there  are  no 
proofs  of  any  remarkable  diminution  of  rainfall  in  Urambo.  Capt. 
Lugard  2  reports  that  the  year  1891-92  was  a  wet  one  on  the  shores 
of  the  Victoria  Xyanza,  and  the  lake-level  had  risen  6  feet  above 
the  normal.  Dr.  Merensky 3  expresses  some  doubts  concerning  the 
diminution  of  Lake  i^yassa  reported  by  so  many  British  travellers. 
These  reports  point  perhaps  to  the  first  traces  of  a  rise  of  level 
beginning  in  the  African  lakes,  and  so  it  appears  the  more  highly 
desirable  to  continue  regularly  and  patiently  all  such  observations 
as  may  serve  to  elucidate  the  phenomena  in  question. 
1  Peterm.  Mittheil.  vol.  xxxix.  (1893)  pp.  47  et  seqq. 
2  Proe.  Boy.  Geogr.  Soc.  1892,  p.  827. 
3  Peterm.  Mittheil.  vol.  xxxviii.  (1892)  p.  250. 
