114         On  the  History  of  the  Mechanical  Theory  of  Heat. 
dissipated  during  the  cycle."  The  place  which  he  cites  as  that 
in  which  Thomson  had  given  this  expression  is  the  above-men- 
tioned article  "  On  a  Universal  Tendency  "  &c*  But  in  that 
article  there  is  neither  the  above-quoted  nor  any  equivalent  ex- 
pression ;  in  it  altogether  only  four  formulae  occur,  which  are 
totally  different.  Therefore  Mr.  Tait's  assertion  and  the  accom- 
panying citation  are  to  me  inexplicable. 
In  a  later  memoir  f  I  carried  the  considerations  to  still  greater 
completeness.  The  above  proposition  on  uncompensated  trans- 
formations, which  by  omitting  the  symbol  N  can  be  written 
referred  only  to  circular  processes.  I  now  endeavoured  to 
obtain  a  quantity  valid  for  any  alteration  of  a  body,  and  whose 
value  can  only  change  in  one  direction.  For  this  purpose,  to 
the  hitherto  considered  two  sorts  of  transformation  (viz.  the  trans- 
formation of  work  into  heat  and  vice  versa,  and  the  passage  of 
heat  from  a  warmer  into  a  cooler  body  and  vice  versa)  I  added  a 
third  relative  to  the  change  of  state  of  a  body,  and  represented 
by  the  quantity  Z ;  this  I  named  the  disgregation  of  the  body. 
With  the  aid  of  this  quantity  and  H,  denoting  the  heat  actually 
present  in  the  body,  I  was  able,  in  place  of  the  above  relation, 
to  construct  the  following  more  general  one : — 
It  was  the  sum 
P^M^oj. 
J    T  +  PZ 
for  which  I  introduced  the  name  entropy  of  the  body§.  By  ap- 
plying this  new  idea  I  was  able  to  express  the  tendency  of  nature 
to  transformation,  more  completely  and  definitely  than  it  had  hi- 
therto been  expressed  by  any  one,  in  the  short  proposition  : — 
The  entropy  of  the  universe  tends  to  a  maximum. 
From  the  foregoing  it  will  be  sufficiently  evident  that  the  theory 
of  the  dissipation  of  energy,  or  entropy,  was  not  developed  by 
Thomson  alone,  but  that  I  had  an  essential  share  in  its  develop- 
ment.    How  novel  my  treatment  of  the  subject  was,  compared 
*  Phil.  Mag.  S.  4.  vol.  iv.  p.  304;  and  Proc.  R.  S.  Edinb.  1852. 
t  Pogg.  Ann.  vol.  cxvi.  (1862)  p.  73  ;  Phil.  Mag.  S.  4.  vol.  xxiv.  pp.  81 
&  201 ;  Mechanical  Theory  of  Heat,  p.  215. 
X  Pogg.  Ann.  vol.  cxvi.  p.  109;  Mechanical  Theory  of  Heat,  p.  247. 
§  Pogg.  Ann.  vol.  cxxv.  (1865)  p.  390;  Mechanical  Theory  of  Heat, 
p.  357. 
