﻿Chemistry 
  and 
  Physics. 
  381 
  

  

  The 
  second 
  and 
  third 
  chapters 
  constitute 
  the 
  first 
  and 
  second 
  

   parts 
  of 
  the 
  author's 
  experimental 
  investigations. 
  In 
  the 
  first 
  

   part 
  he 
  enters 
  into 
  the 
  details 
  of 
  the 
  new 
  experiments 
  at 
  some 
  

   length 
  and 
  endeavors 
  to 
  correlate 
  the 
  observations 
  that 
  have 
  

   been 
  heretofore 
  disputed. 
  For 
  example, 
  he 
  studied 
  the 
  depend- 
  

   ence 
  of 
  the 
  variations 
  in 
  the 
  appearance 
  of 
  the 
  discharge 
  and 
  

   of 
  the 
  number 
  of 
  discharges 
  per 
  second 
  upon 
  the 
  resistance 
  of 
  

   the 
  circuit, 
  the 
  effect 
  of 
  blowing 
  streams 
  of 
  air 
  across 
  the 
  spark- 
  

   gap 
  in 
  various 
  directions 
  and 
  through 
  perforations 
  in 
  hollow 
  

   spherical 
  brass 
  electrodes, 
  etc. 
  The 
  second 
  part 
  of 
  the 
  research 
  

   pertains 
  to 
  a 
  special 
  manifestation 
  of 
  the 
  continuous 
  spark, 
  

   so-called. 
  In 
  it 
  the 
  author 
  adduces 
  experimental 
  evidence 
  to 
  

   substantiate 
  his 
  hypothesis 
  that 
  the 
  emission 
  accompanying 
  the 
  

   pilot 
  spark 
  of 
  a 
  discharge 
  in 
  a 
  circuit 
  containing 
  very 
  high 
  

   resistance 
  has 
  such 
  characteristics 
  as 
  show 
  its 
  close 
  relation 
  to, 
  

   but 
  not 
  its 
  identity 
  with, 
  the 
  discharge 
  in 
  rarefied 
  gases. 
  

  

  On 
  the 
  whole, 
  the 
  work 
  is 
  valuable 
  not 
  only 
  as 
  a 
  contribution 
  

   to 
  the 
  experimental 
  side 
  of 
  the 
  subject 
  but 
  also 
  because 
  of 
  the 
  

   unifying 
  point 
  of 
  view 
  attained. 
  On 
  the 
  other 
  hand, 
  the 
  con- 
  

   clusions 
  reached 
  seem 
  to 
  be 
  lacking 
  somewhat 
  in 
  finality 
  for 
  the 
  

   reasons 
  that 
  the 
  colors 
  were 
  not 
  analyzed 
  spectroscopically 
  and 
  

   the 
  number 
  of 
  gases 
  studied 
  was 
  not 
  sufficient 
  to 
  afford 
  material 
  

   for 
  broad 
  generalizations. 
  h. 
  s. 
  u. 
  

  

  8. 
  Ions, 
  Electrons, 
  and 
  Ionizing 
  Radiations; 
  by 
  James 
  

   Arnold 
  Crowther. 
  Pp. 
  xii, 
  276, 
  with 
  95 
  figures. 
  New 
  York, 
  

   1919 
  (Longmans, 
  Green 
  & 
  Co.). 
  — 
  "The 
  present 
  volume 
  is 
  in- 
  

   tended 
  solely 
  as 
  a 
  text-book 
  from 
  which 
  students 
  who 
  have 
  been 
  

   grounded 
  in 
  the 
  more 
  elementary 
  portions 
  of 
  Physics 
  might 
  

   obtain 
  a 
  systematic 
  knowledge 
  of 
  its 
  latest 
  developments. 
  ' 
  ' 
  The 
  

   material 
  selected 
  may 
  be 
  roughly 
  classified 
  as 
  pertaining 
  to 
  (a) 
  

   the 
  nature 
  and 
  properties 
  of 
  ions 
  and 
  electrons, 
  and 
  the 
  phe- 
  

   nomena 
  involved 
  in 
  electric 
  discharges 
  in 
  gases 
  at 
  atmospheric 
  

   pressure 
  and 
  at 
  lower 
  pressures, 
  (b) 
  a-, 
  ,#-, 
  y-, 
  and 
  X-rays, 
  (c) 
  

   radio-activity, 
  and 
  (d) 
  the 
  electron 
  theory 
  of 
  matter. 
  

  

  The 
  classical 
  experiments 
  of 
  J. 
  J. 
  Thomson, 
  Kaufmann, 
  and 
  

   others 
  are 
  deservedly 
  described 
  at 
  some 
  length, 
  whereas 
  less 
  

   epoch-making 
  investigations 
  are 
  wisely 
  presented 
  with 
  more 
  

   emphasis 
  on 
  the 
  general 
  principles 
  involved 
  than 
  on 
  the 
  precise 
  

   details 
  of 
  the 
  experiments 
  as 
  actually 
  performed 
  by 
  any 
  one 
  

   individual. 
  To 
  avoid 
  undue 
  distraction 
  of 
  attention 
  the 
  author 
  

   has 
  reduced 
  the 
  mathematical 
  analysis 
  to 
  a 
  minimum. 
  The 
  

   diagrams 
  and 
  type 
  are 
  large 
  and 
  clear, 
  and 
  the 
  number 
  of 
  

   mechanical 
  errors 
  is 
  very 
  small. 
  The 
  chief 
  adverse 
  criticism 
  

   that 
  can 
  be 
  made 
  fairly 
  is 
  that 
  certain 
  parts 
  of 
  the 
  text 
  are 
  not 
  

   presented 
  in 
  an 
  up 
  to 
  date 
  manner, 
  thereby 
  incurring 
  the 
  risk 
  

   that 
  the 
  student 
  may 
  acquire 
  impressions 
  which 
  will 
  subse- 
  

   quently 
  have 
  to 
  undergo 
  appreciable 
  modification 
  and 
  correc- 
  

   tion. 
  This 
  remark 
  applies 
  especially 
  to 
  the 
  chapter 
  (X) 
  on 
  

   X-rays. 
  h. 
  s. 
  u. 
  

  

  