in  its  Effect  on  Cultivation. 
3 
7.  By  consulting  the  table  it  will  appear  that  the  mean  annual 
temperature  of  the  south-western  coast  of  England  at  the  level  of 
the  sea  is  about  52°,  and  under  nearly  similar  circumstances  at 
the  Orkney  Islands,  from  carefully  recorded  observations,  it  is 
found  to  be  46° • 3 ; thus  there  is  a decrease  of  annual  temperature 
amounting  to  5 ° 7 from  the  southern  to  the  northern  extremity 
of  Great  Britain,  extending  through  9°  of  latitude,  or  635  English 
miles,  which  gives  a decrease  of  one  degree  for  every  1 1 1 miles. 
An  intermediate  point  on  the  sea-coast  will  serve  to  test  this  rate 
of  diminution.  At  Whitehaven,  for  instance,  which  is  300  miles 
from  the  south  coast,  the  ratio  of  decrease  stated  amounts  to 
2° -8,  which  deducted  from  the  temperature  of  the  south  coast 
52°,  gives  49°  *2  for  Whitehaven,  a very  near  approximation  to 
the  observed  mean  temperature  49°  '09. 
8.  The  mean  temperature  increases  from  the  eastern  to  the 
western  coasts:  at  Greenwich  it  is  49°,  at  Penzance  51°  8,  at 
Cork  54°  • 4,  being  at  the  rate  of  one  degree  increase  for  every 
66  miles.  Thus  the  mean  temperature  of  the  British  Islands 
increases  from  east  to  west,  twice  as  much  in  the  same  distance 
as  it  does  from  north  to  south,  other  things  being  equal. 
9.  The  annual  amount  of  heat,  indeed,  on  the  coast  line  of 
Great  Britain,  is  remarkably  equal : at  Penzance  the  mean  tem- 
perature is510,8;  Gosport,  51°-8;  Boston,  49°'6;  Leith,48°-3; 
Aberdeen,  49° * 1 ; Glasgow,  49° • 2 ; Whitehaven,  490,1;  Isle 
of  Man,  49°  • 8 ; Dublin,  49° -1  ; and  at  Swansea  51°.  Thus  on 
a coast  line  of  about  2000  miles,  the  variation  is  only  4°. 
10.  In  passing  from  the  coast  inland,  a considerable  diminution 
of  temperature  often  takes  place.  Leaving  Aberdeen  at  49°  • 1, 
47° '3  is  found  at  Clunie  Manse,  and  45°  at  Alford,  and  that 
within  a distance  of  25  miles.  In  the  middle  of  England  the 
mean  of  the  year  is  also  from  2°  to  4°  colder  than  places  situated 
on  the  coast : this  arises  partly  from  the  effect  of  elevation,  and 
from  the  modifying  influences  of  sea-breezes  which  the  coast 
lands  enjoy. 
11.  The  annual  mean  temperature  of  a country  is,  however, 
but  a slender  criterion  from  which  to  form  an  estimate  of  its 
climate,  and  is  especially  defective  when  the  influence  of  climate 
on  vegetation  is  considered.  Penzance  and  Vienna  have  the  same 
mean  temperature ; but  the  country  around  Vienna — the  upper 
Hungarian  plain — has  a summer  temperature  10°  above  Pen- 
zance. In  the  excessively  cold  winter  of  1796,  when  the  Thames 
was  frozen,  the  temperature  of  the  year  in  this  country  fell  short 
of  the  average  by  only  1°.  M.  Arago  states  that,  in  the  two  years 
1815  and  1816,  the  latter  of  which  was  destructive  to  the  crops 
in  a great  part  of  France,  the  annual  temperature  varied  only 
2°  from  the  standard.  It  is  more  a change  in  the  distribution  of 
b 2 
