in  its  Effect  on  Cultivation. 
64  7 
gradually  appear  (o  increase  in  size,  on  account  of  the  less  pres- 
sure they  bear ; so  that  the  spaces  they  occupy  may  be  repre- 
sented as  follows,  where  the 
adjoining  figure  represents  the 
pile,  and  the  distances  a to  b, 
b to  c,  c to  d,  & c.,  the  distances 
occupied  by  each  layer  of 
fleeces.  It  is  also  evident  that 
the  weight  would  be  greatest 
upon  the  pile  at  a a,  and  de- 
crease to  nothing  on  the  layer 
jj.  Now,  the  same  law  that 
is  so  evident  in  the  layers  of 
wool,  holds,  but  with  much 
more  accuracy,  with  the  air.  At 
the  level  of  the  sea  it  occupies 
a space  which  bears  a pressure 
from  the  superior  air  equal  to  the  weight  of  a column  of  mercury 
of  30  inches  in  height,  or  one  of  water  of  the  height  of  nearlv 
33  feet.  Now,  supposing  each  layer  of  wool  to  have  diffused 
through  it  an  equal  quantity  of  anything — say  oil  or  water — then 
it  is  evident  that  this,  like  the  wool,  would  exist  in  far  greater 
proportion  in  the  same  space  from  a to  b,  than  it  would  from 
i to  j ; and  if  a fleece  were  taken  from  the  lower  pile,  and  placed 
in  the  higher,  the  same  moisture  would  then  be  spread  over  all 
the  space  from  i to  j,  that  had  previously  occupied  the  much 
smaller  space  from  a to  b.  A similar  result  follows  if  a quantity 
of  air — say  a cubic  foot — were  taken  from  the  surface  of  the 
earth,  and  liberated  at  the  height  of  14,000  to  15,000  feet- — -it 
would  expand  into  double  its  volume;  and  the  same  heat  that 
occupied  only  one  foot  on  the  surface  of  the  earth,  would  occupy 
two  feet  at  that  elevation  : and  if  the  temperature  had  been 
60  on  the  surface  of  the  ground,  that  temperature  would  only 
be  30D  at  the  height  where  it  expanded  into  twice  its  volume. 
Again,  if  this  foot  of  air  was  by  mechanical  means  made  to 
occupy  only  half  a foot,  the  same  heat  would  then  give  a 
temperature  of  120’,  and  by  this  means — viz.,  forcing  down  a 
piston  in  a tube,  and  thus  compressing  the  air — a match  at  the 
bottom  of  the  tube  may  be  set  on  fire. 
This,  then,  may  suffice  to  show  the  effect  of  elevation  on 
temperature,  but  with  respect  to  the  lateness  of  harvest,  &c.,  it 
requires  a little  more  investigation. 
At  the  equator,  if  we  ascend  a lofty  mountain,  we  shall  find 
every  variety  of  vegetation ; at  its  base  the  aromatic  trees  of  the 
torrid  zone;  higher  up,  the  sugar-cane  and  coffee-tree;  still 
higher  again,  the  olive  and  fig.  Then  the  vines  of  France  and 
