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  XXV. 
  Notices 
  respecting 
  New 
  Books. 
  

  

  Cours 
  de 
  Physique. 
  By 
  H. 
  BotJASSE. 
  Vols. 
  II., 
  IV., 
  & 
  V. 
  

   Paris 
  : 
  Librairie 
  Ch. 
  Delagrave. 
  

  

  TO 
  compile 
  a 
  new 
  textbook 
  of 
  physics 
  at 
  the 
  present 
  day 
  is 
  no 
  

   light 
  task, 
  since 
  the 
  subject 
  is 
  being 
  enriched 
  in 
  so 
  many 
  ways 
  

   in 
  consequence 
  o£ 
  modern 
  discoveries 
  on 
  both 
  the 
  experimental 
  and 
  

   the 
  theoretical 
  sides. 
  M. 
  Bouasse 
  himself 
  has 
  felt 
  this 
  especially 
  

   in 
  connexion 
  with 
  the 
  development 
  of 
  Thermodynamics 
  (Vol. 
  II.). 
  

   The 
  happy 
  time 
  is 
  past 
  when 
  the 
  lot 
  of 
  a 
  professor 
  was 
  merely 
  to 
  

   explain 
  certain 
  general 
  principles 
  and 
  apply 
  them 
  to 
  some 
  stereo- 
  

   t}'ped 
  examples 
  ; 
  or 
  rather, 
  as 
  we 
  should 
  prefer 
  to 
  say, 
  the 
  happy 
  

   time 
  has 
  come 
  when 
  that 
  is 
  no 
  longer 
  necessary. 
  

  

  The 
  present 
  textbook 
  is 
  one 
  which 
  deals 
  mainly 
  with 
  the 
  

   theoretical 
  side, 
  though 
  the 
  results 
  of 
  theory 
  are 
  usually 
  illus- 
  

   trated 
  by 
  numerical 
  calculations 
  applied 
  to 
  particular 
  experimental 
  

   cases. 
  M. 
  Bouasse 
  possesses 
  the 
  quality 
  of 
  most 
  Trench 
  writers 
  

   of 
  being 
  a 
  very 
  lucid 
  exponent 
  of 
  his 
  subjects. 
  The 
  general 
  im- 
  

   pression 
  conveyed 
  by 
  these 
  volumes 
  is 
  that 
  they 
  are 
  very 
  tightly 
  

   packed 
  ; 
  there 
  is 
  nothing 
  prolix, 
  at 
  any 
  rate, 
  in 
  their 
  style 
  ; 
  and 
  

   yet 
  we 
  do 
  not 
  know 
  of 
  any 
  clearer 
  exposition 
  than 
  we 
  are 
  here 
  

   presented 
  with. 
  Our 
  own 
  preference 
  is 
  that 
  the 
  experimental 
  

   side 
  should 
  be 
  considered 
  side 
  by 
  side 
  with 
  the 
  theoretical, 
  and 
  the 
  

   absence 
  of 
  experimental 
  details 
  may 
  be 
  thought 
  by 
  others 
  as 
  well 
  

   as 
  ourselves 
  to 
  be 
  a 
  drawback. 
  On 
  the 
  understanding, 
  however, 
  

   that 
  the 
  book 
  is 
  not 
  intended 
  to 
  be 
  used 
  alone, 
  we 
  can 
  confidently 
  

   recommend 
  it. 
  The 
  parts 
  of 
  the 
  subject 
  which 
  are 
  dealt 
  with 
  in 
  

   the 
  volumes 
  at 
  present 
  before 
  us 
  are 
  : 
  Thermodynamics, 
  Theory 
  of 
  

   Ions, 
  Optics, 
  Electro-optics, 
  Hertzian 
  Waves. 
  

  

  The 
  Theory 
  of 
  Valency. 
  By 
  J. 
  Newton 
  !Fkie3»d. 
  

   Longmans, 
  Green 
  & 
  Co. 
  1909. 
  Price 
  5s. 
  

   This 
  forms 
  one 
  of 
  the 
  Textbooks 
  of 
  Physical 
  Chemistry 
  edited 
  by 
  

   Sir 
  "\Ym. 
  Eamsay. 
  The 
  fact 
  that 
  a 
  special 
  volume 
  should 
  be 
  

   needed 
  dealing 
  with 
  a 
  peculiar 
  part 
  of 
  a 
  subject 
  like 
  this, 
  is 
  

   sufficient 
  evidence 
  of 
  the 
  very 
  rapid 
  progress 
  of 
  knowledge. 
  No 
  

   volume 
  on 
  this 
  subject 
  exists 
  prior 
  to 
  this 
  one 
  in 
  English, 
  and 
  only 
  

   one 
  in 
  German 
  : 
  consequently 
  it 
  practically 
  opens 
  new 
  ground 
  in 
  

   the 
  way 
  of 
  separate 
  publication. 
  The 
  subject 
  is 
  a 
  very 
  fascinating 
  

   one, 
  and 
  our 
  author, 
  who 
  can 
  speak 
  with 
  weight, 
  has 
  put 
  it 
  

   forward 
  in 
  an 
  interesting 
  and 
  thorough 
  fashion. 
  In 
  spite 
  of 
  the 
  

   many 
  difficulties 
  which 
  the 
  subject 
  presents, 
  there 
  can 
  be 
  no 
  doubt 
  

   that 
  the 
  idea 
  of 
  valency 
  is 
  a 
  valuable 
  one, 
  especially 
  in 
  the 
  light 
  of 
  

   modern 
  electrical 
  developments. 
  At 
  the 
  same 
  time 
  the 
  present 
  

   reviewer 
  wonders 
  whether 
  it 
  is 
  not 
  being 
  pressed 
  too 
  far. 
  The 
  

   possibility, 
  at 
  any 
  rate, 
  of 
  the 
  existence 
  of 
  fractional 
  valencies 
  is 
  

   certainly 
  suggested 
  by 
  the 
  phenomena 
  of 
  loose 
  aggregates 
  such 
  as 
  

   in 
  the 
  formation 
  of 
  hydrates. 
  It 
  also 
  is 
  suggested 
  by 
  such 
  results 
  

   as 
  those 
  of 
  Ternent 
  Cooke 
  (p. 
  57), 
  according 
  to 
  which 
  the 
  vapour 
  

  

  