4 
On  the  Climate  of  the  British  Islands 
heat  through  the  different  months,  than  a change  in  the  mean 
temperature,  that  disappoints  the  expectation  of  the  husbandman 
and  causes  a scanty  crop. 
12.  In  endeavouring  to  trace  the  increase  of  winter  cold  from 
south  to  north,  an  extraordinary  fact  springs  up  on  the  very 
threshold  of  the  inquiry,  viz.,  that  the  month  of  January  is  warmer 
at  the  north  of  Scotland  than  in  the  country  round  London.  At 
Greenwich  and  Chiswick  the  mean  of  the  month  is  36°  and  37°, 
whilst  at  Wick  it  is  380,5;  at  the  Orkney  Isles,  39° * 5 ; and  at 
Shetland  40°.  The  intermediate  points  on  the  coast  line  also 
confirm  this  remarkable  distribution  of  heat ; the  January  tem- 
perature of  Glasgow  on  the  west,  and  of  Aberdeen  on  the  east 
coast,  being  38°.  The  cold  winters  of  some  of  the  northern  and 
o 
midland  districts  result  rather  from  their  position  and  elevation 
than  from  any  difference  in  latitude.  The  country  extending  from 
London  through  the  middle  of  England  to  York,  including  the 
parallel  eastern  coast,  has  the  lowest  winter  temperature  of  the 
kingdom  in  proportion  to  its  altitude.  Passing  from  this  district 
to  the  western  coast,  a considerable  increase  of  the  January  tem- 
perature takes  place : at  Liverpool  it  is  4°  higher  than  at  Boston, 
on  the  opposite  side  of  England.  Further  south  this  progression 
may  be  more  definitely  traced ; thus  the  mean  of  January  at 
Greenwich  is  35°*5;  Chiswick,  37°;  Isle  of  Wight,  38°;  Truro, 
Helston,  and  Penzance  420,6;  northward  at  Swansea  it  is  42°; 
and  from  thence  to  Cork  it  rises  to  44°.  The  warmest  winter 
temperature  is  therefore  found  on  the  south-west  coast  of  Eng- 
land, and  in  South  Wales;  but  it  is  more  particularly  evident  on 
the  low  lands  of  the  south  coast  of  Ireland. 
13.  The  increase  of  winter  cold  in  various  parts  of  these 
islands  (and  which  is  often  so  severe  as  to  convert  a productive 
soil  in  one  position  into  a state  of  comparative  barrenness  in 
another)  cannot  mainly  be  attributed  to  a difference  of  latitude, 
for,  as  has  been  shown,  where  all  things  are  equal,  as  on  the  sea 
coast,  a great  equality  of  temperature  prevails.  It  is  now  satis- 
factorily ascertained  that  the  temperature  of  different  places  in 
this  kingdom  is  affected  less  by  latitude  than  any  other  part  of  the 
world  within  the  same  isothermal  zone.  The  lines  of  mean  tem- 
perature of  41°  and  50°,  laid  down  by  Humboldt,  fully  demon- 
strate this.  But  when  the  true  position  of  these  lines  is  more 
accurately  determined  by  the  valuable  tables  of  Professor  Dove,* 
their  want  of  parallelism  becomes  much  more  apparent— this 
zone  of  temperature  on  the  American  coast  being  only  about 
300  miles  wide ; but  at  the  British  Isles  it  is  extended  to  a width 
of  1100  miles,  a striking  proof  of  the  equable  nature  of  our 
See  the  chart  which  accompanies  this  Essay. 
