516  Prof.  Tait  on  the  History  of  the  Second  Law 
merits  have  convinced  me  that  it  was  sufficient  for  all  practical 
purposes  to  determine  the  rise  of  the  thermometer,  in  the  case 
of  a  saturated  atmosphere,  for  two  extreme  points  only,  such  as 
0°  and  20°  R.,  and  to  distribute  this  difference  equally  between 
the  intermediate  degrees.  It  also  appeared  to  me  that  the  va- 
riations of  the  thermometer,  at  the  moment  of  its  being  with- 
drawn from  the  acid,  were  proportional  to  the  tensions  of  the 
vapour  at  the  above  temperatures. 
"  It  might  appear  probable  at  first  sight  that,  however  small 
the  quantity  of  vapour  contained  in  the  atmosphere,  there  would 
always  be  a  sufficient  quantity  of  moisture  to  saturate  the  acid 
film  spread  over  the  surface  of  the  bulb,  and  consequently  to 
develope  in  every  case  an  equal  quantity  of  heat.  My  answer 
to  that  objection  is,  that  there  appears  to  exist  a  sort  of  opposi- 
tion between  the  affinity  of  the  acid  for  moisture  and  the  ten- 
dency of  water  to  remain  in  a  state  of  aqueous  vapour,  which 
increases  in  proportion  to  the  dryness  of  the  atmosphere.  It 
follows  that  the  greater  the  quantity  of  moisture  contained  in 
the  atmosphere  the  greater  the  rapidity  with  which  it  will  be 
condensed  by  the  acid,  and  consequently  the  greater  the  heat 
developed.  The  thermometer  in  each  case  will  continue  rising 
until  the  cooling  influence  of  the  surrounding  air  becomes  suffi- 
cient to  neutralize  the  quantity  of  heat  due  to  the  condensation 
of  moisture,  and  the  moment  at  which  that  effect  is  produced 
must  depend  upon  the  greater  or  less  quantity  of  vapour  the 
atmosphere  contains." 
LXIV.   On  the  History  of  the  Second  Law  of  Thermodynamics , 
in  reply  to  Professor  Clausius.     By  Professor  Tait*. 
PROFESSOR  CLAUSIUS  seems  to  forget  that  it  was  he 
who  raised  this  discussion,  and  that  he  used  the  words 
"  Absichtlichkeit,"  "sehr  geschickt  abgefasst,"  &c.  Such  lan- 
guage may  amaze  and  amuse ;  it  is  too  reckless  to  produce  irri- 
tation. Does  Professor  Clausius  seriously  suppose  that  Thomson, 
Clerk-Maxwell,  and  myself  have  been  deliberately,  by  suppression 
and  by  special  pleading,  attempting  to  deprive  him  of  his  just 
claims  ?  So  desirous  was  I  to  do  him  full  credit  that,  when  he 
(in  correspondence)  objected  to  a  remark  which  is  certainly  in 
substance  correct,  and  which  would  otherwise  have  appeared  in 
my  little  work,  I  requested  a  friend  who  is  thoroughly  acquainted 
with  Professor  Clausius's  papers  to  rewrite  for  me  the  greater 
part  of  the  pages  bearing  on  them. 
I  am  happy  to  find  that  Professor  Clausius  has  now  moderated 
his  tone,  and  that  he  does  not  repeat  his  pretensions  to  a  share 
*  Communicated  by  the  Author. 
