106  Prof.  Clausius  on  the  History  of 
I  much  question  whether  we  shall  have  any  data  truly  applicable 
for  calculating  the  amount  of  force  required  to  produce  the  dif- 
ferential motions  observed  in  glaciers. 
I  am  yours  &c, 
Edward  Vansittart  Neale. 
Hampstead,  January  8,  1872. 
XIII.  A  Contribution  to  the  History  of  the  Mechanical  Theory  of 
Heat.     By  Professor  Clausius. 
To  the  Editors  of  the  Philosophical  Magazine  and  Journal. 
Gentlemen^  Bonn,  January  6,  18/2. 
THERE  has  recently  appeared  a  very  valuable  book,  entitled 
"  Theory  of  Heat,  by  J.  Clerk  Maxwell,"  in  which  the  me- 
chanical theory  especially  is  regarded  with  favour,  and  many 
quotations  and  historical  notices  in  reference  to  its  origin  and 
development  are  given.  In  all  these  details,  however  (with  the 
exception  of  the  "  Molecular  Constitution  of  Bodies  n)>  my  wri- 
tings are  left  quite  unmentioned;  and  my  name  occurs  only 
once,  when  it  is  said  that  I  introduced  the  word  entropy ;  but 
it  is  added  that  the  theory  of  entropy  had  already  been  given 
by  W.  Thomson.  Hence  any  one  who  derives  his  knowledge 
of  the  matter  solely  from  this  book  must  conclude  that  I  have 
contributed  nothing  to  the  development  of  the  mechanical  theory 
of  heat.  Since  Professor  Maxwell,  through  his  many  beautiful 
investigations,  justly  enjoys  a  wide-spread  reputation,  I  think 
that,  however  reluctantly  I  resolve  to  do  so,  it  is  yet  incumbent 
on  me  to  say  something  in  order  to  correct  the  representation 
he  has  given.  Considering  that  you  have  done  me  the  honour 
to  admit  into  the  Philosophical  Magazine  nearly  all  my  memoirs 
on  the  mechanical  theory  of  heat,  I  trust  that  also  to  these  per- 
sonal observations,  to  which  I  am  compelled,  you  will  kindly 
grant  a  place  in  your  esteemed  journal. 
I  remain,  Gentlemen, 
Most  respectfully  yours, 
R.  Clausius. 
Por  the  better  understanding  of  the  following,  it  will  be  useful 
first  to  say  something  on  the  condition  of  the  theory  of  heat  at 
the  time  of  the  publication  of  my  first  memoir  relative  thereto. 
In  the  years  1842-49  had  appeared  the  first  splendid  writings 
of  M^yer,  Colding,  and  Helmholtz  on  the  conservation  of  energy, 
and  a  portion  of  the  celebrated  investigations  of  Joule  on  the 
mechanical  equivalent  of  heat,  but  at  that  time  had  not  become 
so  well  known  as  they  deseryed  to  be. 
