648 
Climate  of  the  British  Islands 
Italy,  followed  by  the  oaks,  elms,  &c.  of  England,  succeeded  by 
the  pines  of  Scotland  and  Sweden,  and  then  the  lichens  and 
mosses  of  Lapland,  followed  by  the  region  of  perpetual  snow. 
H ence  the  journey  from  the  base  of  a mountain  to  the  height  of 
16,000  feet  will  be  equivalent,  with  respect  to  its  mean  temperature, 
to  a journey  from  the  equator  to  the  frigid  zone.  Yet  there  will 
be  one  great  and  characteristic  difference — a difference,  in  fact, 
which  makes  a very  important  distinction  in  its  vegetable  culture. 
In  ascending  the  mountain  we  have  a gradual  decrease  of  tem- 
perature, and  this  is  uniform  through  the  year.  Thus,  at  the 
equator,  allowing  the  temperature  to  be  81  ‘5°,  in  going  to  the 
height  of  252  feet  the  temperature  will  be  80"  5°.  In  ascending 
253  feet  higher,  79"  5°,  and  so  on  ; this  temperature  being  uniform 
during  the  whole  year.  On  the  contrary,  and  this  distinction  is 
important  in  its  effect  on  the  growth  of  corn,  in  going  from  the 
equator  to  the  poles  the  same  decrease  of  mean  temperature 
takes  place  as  in  ascending  a mountain,  but  this  is  caused  by  the 
cold  of  winter  increasing  nearly  twice  as  rapidly  and  the  heat  of 
summer  decreasing  in  only  a small  degree.  Thus  Moscow  has 
a degree  of  heat  in  summer  only  12°  inferior  to  that  of  the 
equator,  whilst  the  cold  of  winter  is  greater  by  70°  than  the 
mean  of  the  same  line.  On  this  account,  those  kinds  of  corn 
requiring  but  a short  time  to  arrive  at  maturity  and  perfect  their 
seed  may  grow  near  to  the  pole  during  the  summer,  and  we  accord- 
ingly find  barley  growing  as  far  north  as  70 0 of  latitude  in  Lap- 
land.  Thus,  the  sun  being  above  the  horizon  at  the  pole  for 
six  months  in  the  year,  it  has  been  calculated  by  eminent  mathe- 
maticians that  the  heat  of  summer  at  the  poles  ought  to  be 
greater  than  at  the  equator,  they  considering  that  the  length  of 
time  the  sun  is  above  the  horizon  there  ought  to  make  up  for  the 
obliquity  of  his  rays.  But  though  this  is  not  the  case,  yet,  when 
the  rays  of  the  sun  are  allowed  their  full  effect,  they  have  been 
known  to  set  fire  to  forests  in  Norway  and  Sweden,  and  during 
Sir  John  Franklin’s  expedition  the  heat  was  sufficient  to  melt 
the  pitch  from  the  ships  in  latitude  67°.  On  this  account  it  is 
then,  that  where  places  have  a southern  aspect  corn  can  be 
ripened  though  the  mean  temperature  of  the  year  be  below  the 
freezing  point,  or  farther  north  than  the  isothermal  line  of  32°, 
which  passes  from  Ulea,  in  Lapland,  latitude  66’,  to  Table  Bay, 
in  Labrador,  latitude  54°.  But  it  must  by  no  means  be  inferred 
from  this  that  corn  will  grow  on  elevated  situations  whose  mean 
temperature  is  so  low ; on  the  contrary,  in  the  plains  of  Quito 
corn  will  not  ripen  in  places  having  a mean  temperature  of  55°, 
or  one  equal  to  that  of  France.  Again,  the  olive,  fig,  myrtle, 
vine,  and  mulberry  will  grow  to  the  size  of  the  oak  in  mountain- 
ous situations  in  the  tropics  whose  mean  temperature  is  less  than 
