230  Mr.  J    Stevenson  on  the  Chemical  and 
Irish  Channel  contained  on  the  average  3"08  parts  by  volume 
of  carbonic  acid  in  10,000  parts  o£  air,  that  the  air  of  the 
Atlantic  Ocean  contained  2'd5  parts  and  the  air  of  tropical 
Brazil  3"28  parts.  On  the  other  hand,  Beauvais,  as  quoted  by 
Dr.  Phipson  in  his  book  on  the  '  History  of  the  Atmosphere/ 
states  that  there  is  only  a  trace  of  carbonic  acid  in  the  air 
over  the  ocean,  and  Dr.  Phipson  also  states  that  Dr.  Verhaeghe 
of  Ostend  found  only  2\  parts  of  carbonic  acid  in  100,000 
parts  of  air  at  the  sea-coast,  being  less  than  r]0  of  the 
amount  found  in  inland  districts.  These  results  do  not  accord 
very  well  with  those  of  Professor  Thorpe,  but  still  both  sets 
of  results  indicate  that  sea  air  is  poorer  in  carbonic  acid  than 
country  air;  and  this  conclusion  is  confirmed  by  observations 
taken  regarding  the  influence  of  the  direction  of  the  wind  on 
the  amount  of  carbonic  acid  in  the  atmosphere  at  one  and  the 
same  place.  The  observers  Reiset  at  Dieppe,  Schulze  at 
Postock,  and  Farsky  at  Tabor  in  Bohemia,  all  found  (as 
mentioned  by  Letts  and  Blake  in  their  book  on  the  Carbonic 
Anhydride  of  the  Atmosphere)  that  when  the  wind  was  in  a 
westerly  or  S.W.  direction,  that  is  to  say  when  it  was  coming 
from  the  Atlantic  Ocean,  there  was  less  carbonic  acid  in  the 
atmosphere  than  when  it  came  from  the  east  or  the  north. 
The  figures  obtained  by  Miintz  and  Aubin,  referred  to  in  my 
former  paper,  may  also  be  regarded  as  confirming  the  same 
Supposition.  These  observers  found,  on  making  a  summary 
of  their  results,  that  the  air  of  the  northern  hemisphere  con- 
tained 2'82  parts  by  volume  of  carbonic  acid  in  10,000,  and 
the  air  of  the  southern  hemisphere  contained  2*72  parts  in 
10,000.  It  is  obvious  that  as  a  much  larger  area  of  the 
southern  hemisphere  i^  covered  by  water  than  is  the  case 
with  the  northern  hemisphere,  it  is  permissible  for  us  to  con- 
jecture that  the  difference  observed  by  Miintz  and  Aubin  may 
be  owing  to  that  circumstance. 
It  should,  however,  be  noted  that  the  differences  in  the 
percentage  of  carbonic  acid  in  the  air  observed  at  different 
inland  places  (that  is  at  one  inland  place  as  compared  with 
another),  and  also  the  differences  in  the  percentage  observed 
at  different  places  on  the  sea-coast,  are  or  were  much  greater 
than  the  difference  between  2'72  and  2'82  ;  also  that  the 
daily  and  weekly  variations  or  other  variations  at  longer  or 
shorter  intervals  in  the  percentage  of  carbonic  acid  in  the  air 
at  one  and  the  same  place  are  frequently  greater  than  the 
difference  of  the  above  amounts.  We  cannot  therefore  put 
very  much  stress  on  the  above  figures  until  they  are  con- 
firmed by  fuller  and  more  detailed  research  ;  but  "still  if  we 
simply  accept  the  evidence  as  it  stands,  we  can  say  that   it  is- 
