338  Prof.  P.  G.  Tait  on  the  Dissipation  of  Energy. 
Ions  dispersion,  inasmuch  as  R  cos  a  increases  with  \{c  a  X-1).  In 
this  view  I  cannot  at  all  agree.  Meyer  seems  to  have  overlooked 
the  fact  that  h  (in  his  notation  k)>  the  constant  of  opacity,  is 
subject,  to  enormous  chromatic  variations,  in  comparison  with 
which  those  of  X  may  be  treated  as  quite  insignificant.  But 
this  is  not  all.  It  has  been  laid  down  by  Kundt  as  the  result 
of  his  observations — and  a  very  remarkable  and  suggestive  result 
it  is — that  the  anomalous  effect  is  not  confined  to  those  rays 
which  are  intensely  absorbed.  Probably  indeed  the  effect  va- 
nishes at  that  part  of  the  spectrum  which  corresponds  to  the 
centre  of  the  absorption- band,  where,  according  to  Meyer's  for- 
mula (though  not  his  interpretation  of  it),  it  should  be  a  maxi- 
mum. I  have  already  indicated  what  appears  to  me  to  be  the 
true  mechanical  character  of  the  phenomenon  by  an  illustration 
derived  from  ordinary  dynamics.  The  mathematical  analysis  of 
the  problem  referred  to,  which  turns  up  in  almost  all  branches 
of  physics  dealing  with  vibrations,  is  well  known  and  therefore 
need  not  be  given  here. 
April  5. 
XLI.  Reply  to  Professor  Clausius.     By  P.  G.  Tait*. 
WHEN  Professor  Clausius  succeeds  in  making  his  own 
countrymen  regard  him  as  the  discoverer  of  the  Dissi- 
pation of  Energy  (see,  for  instance,  Helmholtz,  Populdre  wis- 
senschaftlicheVortrdge,  Heft  ii.  p.  117)  it  will  be  time  enough  to 
complain  that  foreigners  do  not  give  him  that  credit. 
As  regards  the  question  to  whom  is  due  the  credit  of  first  cor- 
rectly adapting  Carrjot's  magnificently  original  methods  to  the 
true  theory  of  heat,  it  is  only  necessary  to  compare  the  Axiom 
of  Professor  Clausius' s  first  paper  (the  only  one  which  has  a 
chance  of  priority  over  Thomson)  with  the  behaviour  of  a  thermo- 
electric circuit  in  which  the  hot  junction  is  at  a  temperature 
higher  than  the  neutral  point,  and  where  therefore  heat  does,  of 
itself  pass  from  a  colder  to  a  hotter  body.  A  thermo-electric 
battery,  worked  with  ice  and  boiling  water,  is  capable  of  raising 
to  incandescence  a  fine  wire,  giving  another  excellent  instance 
of  the  fallacy  of  the  so-called  axiom. 
Professor  Clausius  has  rendered  many  services  to  science, 
especially  in  the  Kinetic  Theory  of  Gases ;  but  he  has  done,  and 
seems  to  take  credit  in  doing,  uncompensated  mischief  by  his 
introduction  of  what  he  calls  innere  Arbeit  and  Disgregation. 
In  our  present  ignorance  of  the  nature  of  matter,  such  ideas  can 
do  only  harm;  and  no  one  will  dispute  his  full  claim  to  originality 
as  regards  them, 
*  Communicated  by  the  Author. 
