in  its  Effect  on  Cultivation. 
6?5 
of  the  sen,  and  that  by  winter  I understand  the  months  of 
December,  January,  and  February.  It  is  important  that  whilst 
vegetation  during  nine  months  of  the  year  in  the  middle  and 
eastern  parts  of  England,  is  liable  to  a cold  below  the  freezing 
point,  during  the  night. — in  places  situated  south-west  of  the 
line  of  41°  winter-cold,  they  are  not  liable  to  a cold  so  severe 
during  more  than  four  months  of  the  year.  On  this  account, 
many  tender  plants,  as  the  myrtle  and  camellia,  natives  of 
southern  Europe,  flourish  in  the  open  air  in  some  parts  of 
Cornwall  and  the  south-west  of  Ireland.  On  the  same  account 
it  is  that  the  growth  of  artificial  food  for  cattle  is  much  less 
imperative  there  than  in  the  eastern  parts  of  England,  grass 
growing  all  the  year  round  in  those  districts. 
In  entering  upon  the  next  subject,  viz.,  “ Different  distri- 
bution of  heat  in  the  various  seasons  of  the  year,’’  the  force  of 
the  preceding  observations  will  appear  more  evident.  From 
what  was  before  stated,  the  reader  will  be  prepared  to  hear  that, 
during  the  coldest  month  of  the  year  London  is  colder  than  the 
Orkney  Islands,  whereas  in  the  wrarmest  months  it  is  full  20 
warmer — the  extreme  range  of  the  thermometer  being  only  27°  in 
the  Orkneys,  whilst  the  annual  range  at  London  is  from  20°  to 
81°  of  Fahrenheit,  or  61°. 
With  respect  to  mean  temperature,  it  inav  be  useful  to 
some  to  remark  that  it.  comprises  very  opposite  states  which  may 
be  very  differently  distributed.  At  one  period  of  the  day  in  summer, 
from  noon  to  3 p.m.,  we  may  have  a temperature  of  81°,  equal  to 
what  they  have  at  the  equator,  and  at  midnight  one  of  40°. 
The  general  mean  temperature  of  any  place  is  made  up  of 
the  average  of  those  of  day  and  night  for  each  day : again  an 
average  of  these  averages  for  a month  ; the  average  again  of  three 
months,  for  winter,  summer,  &c.  ; and  again  an  average  of  these 
lor  the  mean  of  the  year.  If  the  above  were  not  the  case,  culti- 
vation would  be  altogether  different.  Were  the  mean  tempera- 
ture of  a place  that  of  every  day  and  hour  through  the  year,  then 
we  should  have  perennial  spring — trees  and  shrubs  that  would 
vegetate  would  be  evergreens;  grass  and  our  numerous  roots 
would  grow  equally  well  at  any  season,  but  corn  would  never 
ripen.  In  England  we  should  have  strawberries,  raspberries, 
and  a few  other  fruits,  but  none  else  would  ever  come  to  maturity, 
aud  it  is  easy  to  see  that  we  should  be  losers  by  the  change. 
Since  the  distribution  of  heat,  through  the  seasons  then  is  so  im- 
portant to  cultivation,  I will  now  state  that  distribution  in  the 
British  Islands,  leaving  generally  the  discussion  of  its  effects  on 
cultivation  till  I come  to  speak  of  the  effect  of  climate  on  different 
cultivated  plants,  &c. 
First,  as  it  respects  the  distribution  of  heat  through  the  dav,  I 
