in  its  Effect  on  Cultivation. 
27 
63.  But  apart  from  instruments,  we  can  judge  of  the  dryness 
of  the  air  by  its  effects.  In  the  west  of  England  a floor  of  stone 
flags  is  as  often  found  with  a wet,  as  with  a dry  surface  ; and 
harness  which  has  been  laid  by  for  a few  days  becomes  covered 
with  moisture.  “ The  worst  circumstance  of  the  climate  of 
Ireland  (says  Arthur  Young)  is  the  constant  moisture  without 
rain.  Wet  a piece  of  leather,  and  lay  it  in  a room  where  there  is 
neither  sun  nor  fire,  and  it  will  not,  in  summer  even,  be  dry  in  a 
month.”  The  mild  temperature  of  Ireland,  and  the  great 
humidity  of  the  air  acting  on  an  open  rich  limestone  soil,  wonder- 
fully promote  vegetable  growth.  The  lowest  degree  of  heat  is 
not  sufficiently  cold  to  check  the  progress  of  the  natural  herbage ; 
nor  the  highest  summer  temperature  in  general  powerful  enough 
to  parch  the  surface  of  the  moist  soil  ; hence  the  land  is  clothed 
with  constant  verdure,  and  merits  the  characteristic  name  which 
it  has  obtained — “ The  Emerald  Isle.” 
Our  ordinary  sensation  and  feeling  is  a good  test  of  humidity. 
In  the  dry  atmosphere  around  London  I have  found  the  system 
braced  and  strengthened.  In  the  midland  counties,  especially 
Northampton,  there  is  a delicious  feeling  of  pureness  and  fresh- 
ness in  the  air,  which  makes  you  inhale  it  with  the  same  delight 
as  that  with  which  the  Hindoo  drinks  the  water  of  the  Ganges. 
But  on  the  Western  shores  the  constant  moisture  relaxes  the 
frame,  the  night  air  is  cold  and  murky,  and  the  chilly  feeling  pro- 
duced, is  scarcely  overcome  by  the  adoption  of  two  evils — the 
overcoat  and  wrapping-shawl. 
64.  Mists. — The  moist  wind  from  the  Atlantic  on  approaching 
the  western  hills  is  driven  up  their  slopes  until  it  reaches  a colder 
stratum  of  air,  and  if  perfect  condensation  does  not  take  place 
the  vapour  becomes  visible,  and  a damp  driving  mist,  mingled 
with  some  rain,  is  formed,  which  often  continues  for  many  days. 
Vegetation  is  everywhere  loaded  with  moisture;  each  blade  of 
grass,  and  each  twig  of  the  tree,  has  suspended  to  it  a drop  of 
water,  which  when  shaken  off  by  the  wind  is  again  formed. 
From  this  cause  cattle-ponds  on  the  summit  of  hills,  when  sur- 
rounded by  trees,  rarely  fail  of  water.  The  soil  also  absorbs  a 
large  quantity  of  water  which  the  rain-gauge  does  not  measure. 
In  cool  summers  these  mists  often  set  in  before  the  harvest  is 
commenced  on  the  high  lands,  when  the  crops  suffer  severely,  and 
there  is  little  hope  of  saving  them  in  good  condition.  Wales, 
the  north  of  Ireland,  and  the  north-west  of  Scotland  are  parts  in 
which  a late  harvest  is  most  injured  from  this  cause. 
65.  Fogs  are  caused  principally  by  the  change  of  temperature 
in  the  24  hours.  The  soil  of  the  plains  and  valleys  is  heated  by 
the  sun  during  the  day  ; evaporation  and  radiation  of  heat  fol- 
low; on  this  warm  moist  atmosphere  the  cold  air  of  higher 
