MOVEMENTS  OF  FLUIDS  IN  POROUS  BODIES. 
353 
with  earth.  A  manometer  is  imbedded  in  the  interior  of  the 
mass,  and  the  whole  is  plunged  in  a  vessel  full  of  water.  The 
water  immediately  penetrates  its  pores  and  drives  out  the  air, 
which,  collecting  in  the  interior,  exercises  a  pressure  upon  the 
manometer  amounting  with  oxyd  of  zinc  to  five  atmospheres,  and 
with  starch  it  exceeds  six  atmospheres.  This  is  not  the  limit  of 
the  greatest  possible  pressure  ;  Jamin  makes  known  the  causes 
which  diminish  it  in  these  cases,  and  proves  that  the  water  is 
forced  into  porous  bodies  with  a  force  which  he  calls  it,  and 
which  is  equal  to  that  of  a  considerable  number  of  atmospheres. 
A  tube  1.20  metres  long,  filled  with  plaster  and  terminated  at 
the  summit  by  an  evaporating  surface,  is  inserted  by  its  base  into 
a  reservoir  closed  and  filled  with  water;  a  vacuum  is  caused, 
measured  by  15  or  20  millimetres  of  mercury,  or  by  200  or  270 
millimetres  of  water ;  and  the  water  appears  even  at  the  upper 
extremity  of  the  tube,  which  proves  that  porous  bodies  are  able 
to  raise  water  higher  than  can  be  done  by  atmospheric  pressure. 
These  facts  cannot  be  explained  by  the  ordinary  laws  of  capil- 
lary attraction,  since  these  bodies  are  not  formed  of  impermeable 
tubes,  but  of  corpuscles  in  juxtaposition,  separated  by  small  empty 
spaces.  Jamin  has  therefore  submitted  the  problem  to  the  calcu- 
lus and  has  come  to  results,  of  which  we  mention  the  following: 
If  in  a  damp  porous  body,  the  water  is  compressed  by  a  pow- 
er of  several  atmospheres,  it  can  congeal  only  at  a  temperature 
below  0^  C*  Consequently  the  old  wood  is  able  to  resist  frost, 
while  the  young  shoots  being  less  dense  are  unable  to  do  so. 
Since  water  in  filtering  through  a  porous  body  is  compressed 
as  it  enters,  and  dilates  again  as  it  runs  out,  it  should  exhibit 
electric  currents  and  many  other  phenomena. 
The  theory  can  not  be  applied  to  non-homogeneous  porous 
bodies.  In  the  extended  memoir  which  he  has  prepared,  Jamin 
discusses  the  complicated  results  which  may  be  occasioned  by 
irregularity  of  structure  ;  he  makes  an  application  of  it  to  wood, 
and  shows  that  the  interior  pressure  must  be  augmented  in  the 
denser  tissues ;  that  the  air  must  come  from  the  larger  tubes, 
which  cannot  serve  for  the  ascent  of  the  sap. 
*  This  fact  has  just  been  demonstrated  by  Mr.  Sorby,  for  water  contained 
in  capillary  tubes  of  a  small  diameter. — J.  nr. 
23 
