in  its  Effect  on  Cultivation. 
623 
To  the  above  general  results  there  are  of  course  endless  varia- 
tions, indeed  the  extent  of  a single  farm  will  frequently  offer 
examples  of  almost  every  inclination.  Some  of  the  more  striking 
exceptions  I may  name.  In  Ireland,  nearly  the  whole  of  the 
counties  of  Kerry,  Clare,  Limerick,  and  Sligo,  slope  to  the  west; 
whilst  Londonderry  and  Antrim  slope  generally  to  the  north. 
In  Scotland,  Dumfriesshire,  Kirkcudbright,  and  Wigton,  incline 
to  the  south;  whilst  Lanarkshire,  Argyleshire,  and  a great  part 
of  Renfrew  slope  towards  the  west.  In  England,  most  of  the 
counties  bordering  on  the  British  Channel  with  Monmouthshire 
and  Herefordshire  slope  to  the  south,  whilst  Cumberland,  Lan- 
cashire, and  Cheshire  slope  generally  to  the  west. 
The  5th  cause  of  the  modification  of  climate,  viz.  height  above 
the  level  of  the  sea,  will  be  treated  of  when  we  come  to  speak  of 
the  “ Effect  of  Elevation  on  Temperature  and  Lateness  of 
Harvest,”  &c.,  to  which  it  properly  belongs. 
6th.  The  effects  of  cultivation  and  drainage  are  subjects  of  vast 
practical  importance.  With  respect  to  the  preceding  causes 
which  modify  climate,  though  it  is  well  to  know  them,  that  we 
may  not  oppose,  but  act  in  unison  with  nature,  yet  their  influence  is 
generally  beyond  our  control ; but  these  last  are  to  a great  extent 
in  our  own  power,  and  so  far  as  their  influence  extends  man  makes 
a climate  for  himself.  When  we  consider  that  it  is  mainly  owing 
to  the  increase  of  heat  that  the  vegetation  of  the  tropical  regions 
is  so  luxuriant,  and  to  its  absence  that  the  frigid  zone  is  so  sterile 
and  unproductive,  it  becomes  important  that  none  of  the  heat 
imparted  to  our  soil  should  be  wasted,  but  rather  husbanded  with 
a care  equivalent  to  its  beneficial  effects  in  increasing  the  pro- 
ductiveness of  our  soils. 
Now,  all  the  rain  that  falls  upon  our  fields  must  either  be 
carried  away  by  natural  or  artificial  drainage,  or,  having  thoroughly 
saturated  the  soil  on  which  it  falls,  he  left  upon  the  surface  to  be 
carried  off  by  evaporation.  Now,  every  gallon  of  water  thus 
carried  off  by  evaporation  requires  as  much  heat  as  would  raise 
five  and  a half  gallons  from  the  freezing  to  the  boiling  point! 
Without  going  to  extreme  cases,  the  great  effects  of  the  heat 
thus  lost  upon  vegetation  cannot  fail  to  be  striking,  and  I have 
frequently  found  the  soil  of  a field  well  drained  higher  in  tem- 
perature from  10°  to  15°  than  that  of  another  field  which  had  not 
been  drained,  though  in  every  other  respect  the  soils  were  simi- 
lar.* I have  observed  the  effects  of  this  on  the  growing  crops, 
* Since  writing  the  text,  1 have  read,  in  the  ‘Quarterly  Review,’  an  article  on 
Draining,  and  in  which  I lind  the  writer  takes  a similar  view  of  the  had  effects  of 
leading  land  undrained  ; and  states,  that  lib.  of  water  evaporated  from  1000  lbs.  of 
soil,  will  depress  the  temperature  of  the  whole  10°.  Now,  the  temperature  of  the 
ground  3 feet  below  the  surface  in  England  is  rarely  more  than  46°  to  48°;  and  hence 
rain  falling  during  summer  often  of  a temperature  of  60°  to  70’,  raises  the  temperature 
2 s 2 
