in  its  Effect  uu  Cultivation. 
5 
climate;  it  therefore  becomes  obvious  that  the  severe  winter 
temperature  of  various  districts  arises  from  other  causes,  amongst 
which  the  most  prominent  is  the  effect  of  elevation. 
14.  Whilst  it  is  really  difficult  to  show  that  latitudinal  dis- 
tance has  any  marked  effect  in  Great  Britain  on  winter  tempera- 
ture, a few  hundred  yards  of  change  of  altitude  produces  an 
increase  of  cold — at  first  detrimental,  and  then  destructive  of 
remunerative  agriculture.  The  trap-rocks  of  Scotland,  so  fertile 
in  low  situations,  present  a scene  of  desolation  on  the  hills.  The 
grauwacke  of  Wales,  yielding  fair  crops  on  the  coast,  becomes 
barren  on  the  mountains.  And  the  rich  granite  soil  on  the  west 
of  Penzance  has  all  its  productive  powers  nullified  on  the  high 
lands  of  Bodinin-moor  and  Dartmoor.  The  effect  of  altitude  on 
climate  is  thus  a practical  as  well  as  an  interesting  question. 
15.  A detailed  inquiry  in  the  “ Encyclopaedia  Britannica,” 
under  the  article  Climate,  gives  the  following  results  for  the 
ascents  due  to  the  decrement  of  one  degree  Fahrenheit  at  the 
surface,  and  at  the  heights  of  1,  2,  3,  4,  and  5 miles;  viz.  300 
feet,  205,  277,  252,  223,  and  192.  This  in  practice  amounts  to 
1°  for  every  100  yards  of  altitude. 
The  comparative  observations  made  at  Geneva  and  St.  Ber- 
nard give  352  feet  for  1°;*  very  nearly  agreeing  with  Humboldt’s 
equatorial  observations.  But  the  rate  of  progression  increases  in 
colder  climates,  and  continental  observations  will  not  apply  to 
the  insular  position  of  these  islands.  It  is  therefore  desirable 
that  observations  made  on  British  hills  should  form  the  basis  of 
our  inquiry.  I have  extracted  accordingly  from  the  ‘ Transac- 
tions of  the  Royal  Irish  Academy  J the  following  observations 
made  by  General  Roy,  and  have  deduced  the  result : — 
Table  II. — Showing  the  effect  of  Elevation  on  the  Temperature  of  the  Air. 
Temperature  by 
Decrease  of 
Place. 
Lat. 
Heights 
Observation,  f 
Difference. 
Temperature 
for 
in  Feet. 
Below. 
Above. 
100  Feet  of 
Elevation. 
o 
o 
o 
o 
Arthur’s  Seat,  Edinburgh 
56 
803 
54 
50-5 
3-5 
0-43 
Glenmore  .... 
56J 
1279 
55 
51  -5 
3-5 
•26 
Bolfrack 
56$ 
1076 
60 
56-75 
3-25 
•31 
Knockfarle  .... 
56* 
1364 
54 
48-5 
5*5 
•40 
Kirk  Yetton  .... 
56^ 
1544 
54-5 
47-25 
7-25 
•46 
Snowdon  ..... 
53 
3555 
CO 
47-75 
12-25 
•37 
6)223 
Mean 
•37 
* First  Report  of  British  Association,  p.  219. 
\ The  scale  of  temperature  used  throughout  this  Essay  is  that  of  Fahrenheit. 
