in  its  Effect  on  Cultivation. 
17 
the  rain  amounts  to  35  and  40  inches  annually  : a much  larger 
quantity,  no  doubt,  falls  on  the  high  lands.  Thus  the  romantic 
lake  districts  of  Cumberland  and  Killarney  have  not  only  a com- 
mon geological  structure  and  origin,  but  are  abundantly  supplied 
with  water  from  the  concurrence  of  the  same  causes. 
41.  These  hills  have  also  a general  south-west  range,  so  that 
the  valleys  are  longitudinally  open  to  the  rain-clouds,  which  favour 
an  increased  fall  of  rain  on  the  low  lands.  Wastdale  and  Seath- 
waite  are  examples  of  the  effects  produced  by  this  arrangement. 
In  respect  to  Cumberland  Mr.  Miller  remarks  that,  “The  moun- 
tains flanking  the  lake  district  valleys  generally  increase  in  alti- 
tude with  great  regularity  towards  the  head  or  eastern  extremity 
of  the  vale  ; and  it  is  here  the  greatest  depth  of  rain  is  invariably 
found.  The  difference  in  the  annual  quantity  between  places 
contiguous  to  each  other,  and  in  the  same  valley,  is  often  remark- 
ably great.  The  amount  increases  rapidly  as  we  recede  from  the 
sea,  and  towards  the  head  of  the  valley  the  incremental  ratio  is 
enormous.  Loweswater,  Buttermere,  and  Gatesgarth,  in  the  same 
line  of  valley,  are  about  two  miles  apart  from  each  other ; yet  in 
1848  Loweswater  has  received  76  inches,  Buttermere  98  inches, 
and  Gatesgarth  133^  inches  of  water.  Here,  in  a space  of  four 
miles,  we  have  a difference  of  57  inches  in  twelve  months,  and  in 
some  years  the  proportional  excess  is  still  greater.”* 
42.  It  is  observable  that  the  rain-clouds,  on  approaching  moun- 
tain bosses,  discharge  a large  portion  of  their  contents  before  they 
actually  reach  the  hills,  so  that  the  low  land  at  the  foot,  and  the 
valleys  on  the  west  and  south  of  the  hills,  often  receive  a larger 
quantity  of  rain  than  the  higher  ground.  Gatesgarth,  Seathwaite, 
and  Wastdale  lie  at  moderate  elevations,  yet  they  receive  enor- 
mous quantities  of  rain.  Tavistock  and  Goodamoor,  at  the  foot 
of  the  Dartmoor  hills,  are  also  remarkably  wet  places. 
43.  From  the  results  obtained  by  the  mountain  gauges,  and 
from  observations  made  by  the  hygrometer,  Mr.  Miller  infers  that 
“ the  humidity  increases  upwards  from  the  earth’s  surface,  and 
that  the  condition,  or  combination  of  conditions,  most  favourable 
for  the  condensation  and  precipitation  of  vapour  in  the  greatest 
abundance  does  obtain  somewhere  about  2000  feet  above  the 
sea-level.” 
The  effect  produced  by  the  elevation  of  the  land  on  the  fall  of 
rain  may  thus  generally  be  stated  : — 
From  the  sea  at  Whitehaven  to  the  wettest  part  of  the  Cum- 
berland Lake  district,  the  annual  quantity  increases  from  47  to 
146  inches. 
From  the  lands  at  an  altitude  of  about  300  feet  in  Cornwall  to 
VOL.  XI. 
Transactions  of  Royal  Society,  1849. 
C 
