ia  its  Effect  on  Cultivation. 
G35 
and  a dense  fog  is  formed,  which  extends  to  the  westward  till  it 
comes  to  the  mountains ; and  after  crossing  them,  the  heat  being 
raised,  the  fog  is  dispersed,  and  the  western  parts  are  clear  and 
serene.  These  fogs  used  to  cause  ague  and  other  diseases,  but 
the  progress  of  cultivation  has  caused  those  diseases  to  disappear. 
The  reason  why  the  same  cause  does  not  occasion  fog  in  the 
southern  part  of  Britain  is,  that  there  the  land,  being  lower,  is 
heated  even  more  than  the  sea,  and  consequently  the  air  in  pass- 
ing over  it  becomes  heated,  and  instead  of  having  its  vapour  con- 
densed in  fog,  it  becomes  able  to  hold  still  more  vapour  in  an 
invisible  form.  Another  cause  of  this  difference  is  the  narrowness 
of  the  German  Ocean  along  the  southern  shores  of  Britain,  which 
does  not  admit  of  the  wind  imbibing  so  much  vapour  in  its  passage 
across  as  it  does  more  northward.  During  the  spring  and  earlv 
summer  months,  then,  fogs  are  more  prevalent  on  the  eastern 
coast  of  Scotland  than  the  western  ; but  this  cause  has  a limited 
influence  on  England  and  Ireland.  In  the  autumn  the  Atlantic 
has  a temperature  higher  than  the  land  ; hence  along  the  whole 
western  coast  fogs  are  prevalent  during  this  season,  and  these  fogs 
continue  often  for  weeks  together,  especially  in  the  western  parts 
of  Ireland,  the  air  being  very  rarely  quite  clear;  but  a kind  of 
cold  moist  haze  overspreads  the  whole  country  during  the 
autumnal  months,  whilst  the  eastern  parts  are  comparatively 
clear  except  during  the  night.  In  Scotland,  particularly  in 
the  northern  parts,  a blasting  kind  of  fog  frequently  spreads 
along  the  banks  of  rivers  and  along  the  low  ground,  which  causes 
great  damage  to  the  corn  crops,  frequently  doing  irreparable 
injury  to  barley,  and  causing  it  to  turn  black,  whilst  it  leaves 
the  oats,  on  account  of  their  greater  hardihood,  comparatively 
unaffected. 
I now  come  to  the  next  subject,  viz.,  “ 5th.  Different  degree  of 
general  Cloudiness  of  the  Sky.” 
Intimately  connected  with  this  subject  is  the  evaporation  from 
the  surface  of  the  earth  ; and  from  what  has  been  stated  in  the 
preceding  article,  it  is  evident  that  the  more  moisture  there  is  in 
the  air,  the  less  evaporation  there  will  be  from  the  surface  of  the 
earth,  but  the  more  cloudiness  of  the  atmosphere.  Thus  the 
evaporation  will  vary  inversely  as  the  atmosphere  is  more  cloudv, 
and  the  evaporation  will  be  the  least  when  the  cloudiness  is 
greatest.  Due  allowance  must  of  course  be  made  for  difference 
of  temperature.  The  cloudiness  will  be  greater,  and  the  days  in 
which  rain  falls  the  more  frequent,  as  the  temperature  is  the 
lowest.  Column  1st  in  the  succeeding  table  gives  the  month; 
2nd,  the  evaporation  from  a surface  of  water  in  the  western,  and 
3rd,  that  in  the  eastern  counties  ; column  4th,  the  rain  in  the  west  ; 
and  5th,  rain  in  the  eastern  parts. 
