618 
Climate  of  the  British  Islands 
other  causes  as  well  as  distance  from  the  equator ; and  the  popular 
sense  in  which  climate  is  used  has  respect  to  eveiy  influence 
operating  on  the  atmosphere.  Thus  we  speak  of  climates  as  hot 
or  cold,  humid  or  dry , varying  or  unvarying,  &c.  ; and  it  is  the 
combination  of  effect  produced  by  the  whole  of  these  and  other 
agencies  which  constitutes  the  climate  of  any  place.  Climate, 
then,  depends  upon  many  causes,  the  principal  of  which  are  the 
following : — 
1st.  Distance  from  the  equator. 
2nd.  A continental  or  insular  situation. 
3rd.  Prevailing  winds. 
4th.  The  inclination  of  the  land. 
5th.  Height  above  the  level  of  the  sea. 
6th.  The  state  of  cultivation  and  drainage. 
First. — Distance  from  the  equator  influences  climate,  inas- 
much as  at  the  equator  heat  and  moisture,  so  essential  to  the  vege- 
tation of  cultivated  plants,  are  present  in  abundance ; and  this 
heat  is  present  during  the  whole  of  the  year,  so  that  cultivation 
receives  no  check.  There  is  no  division  of  the  seasons  into  winter, 
summer,  spring,  or  autumn,  and  no  period  when  the  cultivation 
of  the  ground  is  prevented  by  frost.  The  only  distinction  of  the 
seasons  is  into  wet  and  dry.  At  the  pole,  on  the  contrary,  the 
cold  is  too  severe  to  admit  of  cultivation  in  any  shape  ; and  places 
between  these  are  more  or  less  favourably  situated  for  cultivation, 
as  they  are  nearer  or  farther  from  the  equator. 
Our  islands  lie  between  the  latitudes  of  50°  and  60°,  and  are 
hence  nearer  to  the  pole  than  the  equator,  and  have  hence  less 
than  an  average  proportion  of  the  heat  requisite  for  vegetation. 
Secondly. — A continental  or  insular  situation.  By  a wise  pro- 
vidential arrangement  the  density  of  water  is  greatest  at  about 
40°  of  temperature ; whilst  its  freezing  point  varies  from  28°  to 
32°,  according  to  its  saltness,  fresh  water  freezing  at  32°,  and 
salt  water  requiring  a greater  degree  of  cold  in  proportion  to  the 
more  or  less  saline  matter  it  may  contain.  Hence  it  follows  that 
when  the  waters  of  the  ocean  fall  below  the  temperature  of  40°, 
or  more  correctly  39° *2,  they  will  sink  by  their  specific  gravity, 
and  the  waters  from  below  will  rise  up  to  supply  their  place : 
hence  it  is  easy  to  perceive  that  until  the  whole  column  of  water 
has  been  successively  brought  to  the  surface,  and  cooled  down, 
the  temperature  will  not  fall  much  below  40°  ; and  consequently 
very  deep  waters  will  never  freeze,  at  least  in  temperate  latitudes. 
Again,  in  summer,  the  surface  of  the  water  being  heated  by  the 
rays  of  the  sun,  will  hence  be  rarified,  and  have  its  density  de- 
creased ; consequently  the  warm  water  will  continue  at  the  sur- 
face, and,  were  it  not  for  the  cooling  effects  of  evaporation,  would 
