514  Prof.  A.  de  la  Rive  on  a  New  Hygrometer, 
ing  a  part  of  chemistry,  the  scope  of  which  branch  of  science  as 
ordinarily  understood  might  be  denned  thus  : — "  Chemistry  is 
that  branch  of  the  study  of  matter  which  takes  cognizance  of 
the  changes  produced  by  the  action  of  bodies  on  one  another 
without  involving  any  quantitative  measure  of  energy  of  any 
kind,  but  only  the  observation  of  particular  conditions  (e.  g. 
temperature,  pressure,  &c.)."  Chemistry  will  in  time  mean 
something  wider  than  this ;  it  and  physics  will  be  regarded  as 
coextensive,  and  identical  in  kind  though  not  in  degree, — physics 
taking  cognizance  of  those  actions  where  the  change  in  the  pro- 
perties of  the  bodies  is  small  or  gradual,  chemistry  of  those 
which  are  greater  or  more  rapid ;  so  that  the  chemistry  of  the 
future  may  be  defined  as  "  that  branch  of  the  study  of  surround- 
ing objects  which  relates  to  their  mutual  actions  on  one  another 
so  as  to  produce  fresh  bodies  differing  in  properties  from  the 
original  ones,  such  changes  being  accompanied  by  a  measurable 
transformation  of  potential  into  actual  energy,  or  vice  versa73 — 
physics  being,  in  short,  a  subsection  of  chemistry,  and  a  neces- 
sary preliminary  to  its  study. 
Until  a  copious  store  of  knowledge  be  gained  in  this  almost 
untrodden  realm,  the  materials  are  absent  on  which  to  superin- 
duce an  hypothesis  sufficiently  comprehensive  to  deserve  the  name 
of  theory  (in  the  ordinary  acceptation  of  that  term,  i.  e.  as  one 
speaks  of  the  theory  of  gravitation,  the  developed  hypothesis) . 
But  what  little  is  known  indicates  that  the  atomic  hypothesis 
alone  is  inadequate  to  take  in  all  phenomena;  on  the  other  hand, 
it  is  admitted  by  many  chemists,  and  notably  by  Dr.Williamson, 
that  conceptions  involved  in  this  hypothesis  are  "  not  raised  in 
chemistry  by  any  evidence  whatever ;  "  while  experience  proves 
that  the  language  founded  on  this  hypothesis  has  so  altered  in 
meaning  as  now  to  be  occasionally  applied  in  senses  contradic- 
tory of  the  original  acceptations ;  so  that,  in  fine,  I  see  no  reason 
for  altering  the  final  conclusions  come  to  in  the  paper  examined  (?) 
by  Mr.  Atkinson. 
Laboratory,  St.  Mary's  Hospital,  W., 
June  12,  1872. 
LXIII.   On  a  New  Hygrometer.     By  A.  de  la  Rive. 
To  the  Editors  of  the  Philosophical  Magazine  and  Journal. 
Gentlemen,  Geneva,  June  1,  1872. 
HAVING  just  seen,  in  volume  xx.,  No.  132,  of  the  'Pro- 
ceedings of  the  Royal  Society/  the  description  of  a  "new 
hygrometer"  by  Mr.  Wildman  Whitehouse*,  allow  me  to  state 
that  an  instrument  founded  on  exactly  the  same  principle  was 
*  See  p.  538  of  the  present  Number. 
