ill  its  Effect  on  Cultivation. 
643 
with  a north  or  north-east  wind,  and  because  a south  or  south- 
west wind  coming  after  a north  or  north-east  generally  brings  us 
rain,  therefore  rain  commonly  falls  when  the  barometer  sinks. 
I shall,  before  concluding,  give  the  results  of  my  own  observa- 
tion with  respect  to  the  indications  of  the  barometer,  and  the 
best  rules  I can  for  forming  an  estimate  of  the  state  of  the 
weather  therefrom  ; but  as  rain  depends  for  its  production  en- 
tirely on  the  moisture  in  the  atmosphere,  and  its  condensation 
there,  it  follows  that,  other  things  being  equal,  the  most  rain  will 
fall  when  the  air  is  most  saturated  with  moisture.  If  then, 
instead  of  a barometer,  an  hygrometer  were  used,*  they  would 
know  much  better  when  rain  might  be  expected ; for  with  any 
means  to  determine  the  quantity  of  moisture  in  the  air,  and  a 
barometer  also,  then  when  the  air  is  nearly  saturated  with 
moisture  and  the  barometer  low  at  the  same  time,  rain  is  sure 
to  follow  in  a short  time. 
Winds. — From  what  was  before  stated  under  the  article 
Moisture  of  the  Air,  it  appears  that  the  capacity  of  air  for  retaining 
moisture  is  increased  by  its  heat ; therefore  if  winds  come  from 
any  place  colder  than  our  islands  they  will  be  heated  in  passing 
overhand  therefore  instead  of  causing  rain  will  have  a tendency 
to  promote  evaporation,  and  their  effect  will  be  to  dry  and  cool 
places  over  which  they  pass  : on  the  contrary,  if  winds  come  from 
places  hotter  than  our  islands,  in  passing  over  them  their  moisture, 
if  they  are  near  saturation,  must  be  condensed  and  fall  in  rain; 
but  if  the  moisture  of  the  air  be  condensed  and  fall  in  rain  on  one 
side  of  our  island,  the  rain  may  fall  there  in  considerable  quan- 
tities, and  yet  it  may  be  dry  on  the  opposite  coast. 
During  autumn  and  winter  then,  when  the  temperature  of  the 
sea  is  higher  than  that  of  the  land,  an  eastern  wind  will  bring 
rain  frequently  to  the  eastern  coast,  but  rarely  to  the  midland  or 
western  counties.  Again,  the  land  being  colder  than  the  sea  in 
a greater  ratio  during  the  night  and  till  10  A.M.,  the  most  rain 
will  fall  during  that  time,  and  that  rain  will  generally  cease  and 
the  day  turn  fine  an  hour  or  two  before  noon,  and  this  I have 
observed  to  be  the  case  in  thousands  of  instances,  the  rain 
generally  ceasing  when  the  temperature  of  the  land  was  raised  to 
that  of  the  sea.  Thus,  as  might  be  inferred,  eastern  winds  rarelv 
cause  rain  at  this  season  in  the  western  counties,  but  the  Atlantic 
being  broad  and  the  air  crossing  it  having  time  to  be  fully  satu- 
rated, and  then  being  rapidly  cooled  in  passing  over  the  moun- 
tainous district  of  the  western  counties,  the  fail  of  rain  is  verv 
great  there,  generally  nearly  double  the  quantity  falling  on  the 
eastern  coast,  but  as  there  is  much  more  moisture  brought  bv 
The  best  hygrometer  is,  I believe,  the  wet  and  dry  bulb  thermometer. — Ph.  P. 
