622  Climate  of  the  British  Islands 
narrow  passes  and  glens,  often  attended  by  storms  of  snow  or 
rain. 
The  next  thing  I have  mentioned  as  influencing  the  climate 
of  any  country  is — 4th.  Its  general  inclination.  Every  one  is 
familiar  with  the  fact  that  frost  or  snow  continues  much  longer 
on  the  north  and  north-eastern  side  of  a building,  a fence,  or  a 
hill,  than  it  does  on  their  southern  or  south-western  side.  On 
a more  majestic  scale  this  is  seen  on  the  northern  slope  of 
the  Altaian  Mountains,  contributing  to  the  frosts  of  Siberia; 
also  in  Switzerland,  where  the  south  and  south-western  sides  of 
the  Alps  are  clothed  with  vineyards,  whilst  the  north  and  north- 
eastern are  covered  with  perpetual  snow. 
The  reason  of  this  will  be  evident  on  an  inspection  of  the 
following  figure.  Let  S represent  the  sun,  and  C D B the 
S 
section  of  a mountain.  Then  it  is  evident  that  the  rays  of  the 
sun  which  would  be  spread  over  the  space  C B,  if  it  were  a 
level  surface,  will  fall  exclusively  upon  the  south  side,  C D, 
which  being  shorter  would  be  warmer  than  the  level  surface,  while 
in  the  extreme  case  supposed  none  will  reach  the  north  side, 
D B,  which  would  therefore  be  chilled.  But  during  summer 
the  sun  would,  after  passing  the  west,  be  lost  to  the  south 
side  of  the  mountain,  so  that  a partial  loss  would  there  take 
place  ; an  aspect  therefore  turned  partially  to  the  west  is  pre- 
ferable, for  it  is  better  to  lose  a portion  of  the  morning  rays 
of  the  sun  than  those  of  the  evening.  The  inclination  of  a 
country  is  best  known  by  the  direction  of  its  rivers.  The 
general  inclination  of  the  British  islands  is  east  by  south,  with  a 
range  of  mountains  running  north  by  east  along  their  western 
sides,  and  generally  sloping  abruptly  to  the  west  by  north.  This 
arrangement  has  a great  effect  on  the  climate  of  the  British  Isles. 
The  large  quantity  of  vapour  contained  in  the  winds  which  have 
crossed  the  Atlantic  Ocean  is  condensed  by  crossing  their  sum- 
mits and  falls  in  rain  on  these  hills  and  the  neighbouring  plains. 
This  condensation  of  vapour,  too,  by  giving  out  a large  quantity 
of  latent  heat  causes  a temperature  much  higher  than  from  their 
elevation  we  should  otherwise  expect,  and  renders  those  hills 
generally  well  fitted  for  maintaining  vegetation. 
