112  Prof.  Clausius  on  the  History  of 
the  mechanical  theory  of  heat  (1850).  I  have  since  published, 
besides  those  which  refer  to  electricity  and  to  the  molecular  con- 
stitution of  bodies,  eight  memoirs  on  that  theory,  all  of  which 
have  been  translated  into  English,  and  since  1867  combined  in 
one  work*;  but  all  of  these  have  been  left  by  Mr.  Maxwell  as 
unnoticed  as  the  first. 
To  enter  into  the  contents  of  these  later  memoirs  would  carry 
us  too  far.  I  will  only  permit  myself  to  touch  on  one  other 
point,  viz.  the  theory  which  refers  to  the  dissipation  of  energy,  or 
to  entropy,  because  another  English  author  also,  whom  I  esteem 
highly,  Mr.  Tait,  in  his  e  Sketch  of  Thermodynamics/  attributes 
this  theory  to  W.  Thomson  alone. 
As  already  mentioned,  I  demonstrated  Carnot's  theorem,  mo- 
dified, thus  : — I  laid  it  down  as  a  fundamental  property,  founded 
in  the  essential  nature  of  heat,  that  it  everywhere  exhibits  the 
tendency  to  compensate  existing  differences  of  temperature,  and 
consequently  to  pass  from  warmer  into  cooler  bodies,  but  can 
never,  without  compensation,  pass  from  cooler  into  warmer 
bodies.  There  results  from  my  considerations,  as  a  correspond- 
ing difference,  that  the  transformation  of  heat  into  work  is  only 
possible  with  compensation,  while  the  transformation  of  work 
into  heat  can  be  effected  without  compensation. 
Two  years  later  a  short  article  appeared,  by  Thomson,  "  On  a 
Universal  Tendency  in  Nature  to  the  Dissipation  of  Mechanical 
Energy  "f,  in  which  he  states  the  three  following  propositions 
as  conclusions  which  he  had  drawn  : — 
1.  "  There  is  at  present  in  the  material  world:  a  universal 
tendency  to  the  dissipation  of  mechanical  energy."  • 
2.  "  Any  restoration  of  mechanical  energy,  without  more  than 
an  equivalent  of  dissipation,  is  impossible  in  inanimate  material 
processes,  and  is  probably  never  effected  by  means  of  organized 
matter,  either  endowed  with  vegetable  life  or  subjected  to  the  will 
of  an  animated  creature." 
3.  "Within  a  finite  period  of  time  past  the  earth  must  have 
been,  and  within  a  finite  period  of  time  to  come  the  earth  must 
again  be,  unfit  for  the  habitation  of  man  as  at  present  constituted, 
unless  operations  have  been,  or  are  to  be  performed,  which  are 
impossible  under  the  laws  to  which  the  known  operations  going 
on  at  present  in  the  material  world  are  subject." 
These  propositions  were  certainly  worthy  of  admiration  for 
their  boldness  and  universality ;  but  after  what  had  preceded,  it 
could  not  be  said  that  they  contained  a  new  principle.  Thomson 
himself  designates  them  as  "consequences  which  follow  from 
*  The  ?^echanical  Theory  of  Heat.   By  R.  Clausius.  Edited  by  T.  Archer 
Hirst.     London  :  J.  Van  Voorst, 
f  Proc.  Roy.  Soc.  Edinb.  April  1852  j  and  Phil,  Mag.  S.  4.  vol.  iv.  p.  304. 
