Intelligence  and  Miscellaneous  Articles. 
159 
which  takes  place  in  stretching  and  in  contracting  the  caoutchouc. 
We  know,  in  fact,  that  when  the  permanent  gases  in  expanding 
perform  work  they  become  cooled,  and  the  more  so  the  more  they 
were  heated  while  in  the  compressed  state — and,  further,  that  the 
work  performed  on  compressing  a  gas  by  a  given  amount  is  equal  to 
that  which  it  produces  when  it  expands,  if  there  is  no  loss.  In 
caoutchouc  there  is  no  such  reciprocity,  owing  to  the  small  mobility 
of  the  particles  and  the  resistance  which  they  must  overcome  in 
order  to  displace  themselves.  Part  of  the  force  communicated  to 
them  is  used  up  in  internal  work,  and  during  expansion  is  con- 
verted into  work  ;  and  another  part  is  also  used  and  changed  during 
the  time  of  contraction.  Hence  it  is  that  the  force  used  in  the  ex- 
pansion of  the  caoutchouc  is  not  entirely  reproduced  in  the  contrac- 
tion. Such  a  conclusion  results  from  the  following  observation. 
In  studying  the  elasticity  of  caoutchouc,  I  have  observed  that  on 
adding  given  weights  this  substance  lengthens  to  a  greater  extent  than 
that  by  which  it  shortens  when  they  are  removed.  I  have  recently 
repeated  these  experiments ;  and  the  results  are  contained  in  the 
folio  wins:  Table  : — 
Caoutchouc  thread  6  millims.  in  thickness. 
Length  while  loaded. 
Added. 
Kemoved. 
Difference  of 
the  loads. 
Loads. 
Lengths. 
Permanent 
loads. 
Lengths. 
1 
2 
3 
4 
5 
6 
7 
millims. 
246-72 
310-42 
39620 
.476-58 
537-90 
586-10 
618-60 
1* 
2 
3 
4 
5 
6 
millims. 
254-50 
318-10 
41900 
493-20 
566-40 
622-60 
7-78 
7-68 
22-80 
16-62 
28-50 
36-50 
Each  load  corresponds  to  a  weight  of  640  grammes. 
It  follows  from  the  last  column  of  this  Table,  and  of  others, 
which  for  shortness'  sake  I  will  not  give,  that  when  a  given  load  is 
removed  the  thread  is  less  shortened  than  it  had  been  lengthened 
by  the  addition  of  the  load  ;  and  the  difference  is  greater  the  greater 
the  lengthenings  have  been. 
This  observation  leads  to  the  assumption  that  the  shortenings  are 
smaller  than  the  lengthenings,  not  on  account  of  diminished  elas- 
ticity, but  because  caoutchouc  in  its  contraction  does  not  develope 
*  These  experiments  were  made  by  adding,  one  after  the  other,  all  the 
stretching  loads  until  the  seventh,  and  then  taking  away  one  each  time 
in  the  same  order.  No  1  in  this  column  thus  corresponds  to  a  single  per- 
manent load,  while  all  the  others  were  removed ;  No.  2  corresponds 
to  two  loads  when  the  others  were  removed,  and  so  with  the  other 
numbers. 
