514 
THE  ADMIEALTY  ASTEONOmCAL  EXPEEIMEXT 
The  chief  purpose  of  the  above  Tables  is  to  serve  in  the  reduction  of  isolated  observa- 
tions to  the  daily  mean : we  may  however  at  once  draw  some  interesting  conclusions 
with  reference  to  low  and  high  stations.  Thus  at  the  level  of  the  sea  there  are  two 
regular  and  equal  tides  in  the  barometer,  but  on  the  mountain  there  is  a tendency  to 
lose  the  afternoon  minimum  and  evening  maximum,  and  to  show  in  the  twenty-four 
hours  only  one  unequally-sided  wave,  having  its  minimum  at  5 a.m.,  and  its  maximum 
at  10  a.m. 
On  the  mountain  the  daily  range  of  the  barometer  is  rather  larger  than  at  the  sea- 
level;  and,  as  with  the  wave  feature  already  adverted  to,  is  greater  at  8903  feet,  than  at 
10,702  feet.  Similarly,  with  the  daily  range  of  the  temperature  and  the  dew-point,  they 
are  nearly  three  times  greater  on  the  mountain  than  below,  but  are  rather  greater 
always  at  Guajara  than  at  Alta  Vista. 
In  the  epochs  and  characteristics  of  the  elevated  barometric  maxima  and  minima,  there 
will  be  immediately  perceived  a resemblance  to  the  effects  of  applying  the  usual  cor- 
rection for  “ elasticity  of  vapour,”  to  deduce  the  pressure  of  dry  atmosphere  at  a lower 
station*;  and  on  introducing  the  same  correction  (viz.  the  elasticity  of  vapour  due  to  the 
temperature  of  the  dew-point),  the  above  quantities  become,  for  the 
inch. 
inch. 
inch. 
inch. 
Sea-level  . 
. +-008 
-•004 
+•008 
-•013 
Guajara 
. +-060 
-•009 
+ •023 
-•072 
Alta  Vista  . 
. +-012 
+ •004 
+ •004 
-•021 
Further  illustrations  of  the  effects  of  height  in  the  hourly  variations  are  given  in 
Plate  XXXVI.,  where  the  hourly  readings  of  the  instruments  on  a coiTesponding  day 
above  and  below  are  graphically  represented. 
(2.)  Daily  Means. 
Towards  procuring  the  daily  means  of  barometer,  thermometer,  and  dew-point,  there 
were  never  less  than  four  observations  each  day  on  board  the  yacht,  and  seldom  less 
than  three  on  the  mountain ; these  being  corrected  by  the  foregoing  Tables  of  hourly 
variations,  and  meaned,  are  exhibited  in  the  following  Tables,  and  part  of  them  in 
Plate  XXXVII. 
* See  Mr.  J.  Jouxsox’s  “ Oxford  Observations  ” for  1856. 
