﻿544 
  Notices 
  respecting 
  New 
  Boohs. 
  

  

  From 
  this 
  we 
  see 
  that 
  the 
  absorption 
  coefficient 
  of 
  the 
  7 
  rays 
  

   in 
  carbon 
  decreases 
  at 
  a 
  much 
  slower 
  rate 
  than 
  the 
  pene- 
  

   trating 
  power 
  of 
  the 
  /3 
  rays 
  excited 
  by 
  them. 
  Consequently, 
  

   for 
  beams 
  of 
  the 
  same 
  intensity 
  we 
  shall 
  get 
  a 
  smaller 
  reading 
  

   for 
  the 
  second 
  cause, 
  the 
  less 
  penetrating 
  the 
  7 
  rays, 
  the 
  

   walls 
  being 
  sufficiently 
  thick 
  to 
  give 
  the 
  maximum 
  effect. 
  

   It 
  depends 
  on 
  the 
  ratio 
  of 
  the 
  ionizations 
  due 
  to 
  (1) 
  and 
  (2) 
  

   what 
  value 
  we 
  get 
  when 
  comparing 
  two 
  types 
  of 
  radiation, 
  

   bat 
  it 
  is 
  thought, 
  in 
  the 
  cases 
  dealt 
  with, 
  that 
  the 
  second 
  

   cause 
  gives 
  more 
  ionization 
  than 
  the 
  first, 
  so 
  that 
  the 
  softer 
  

   the 
  beam 
  of 
  y 
  rays 
  the 
  less 
  ionization 
  they 
  will 
  give. 
  As 
  an 
  

   approximation, 
  the 
  ionization 
  is 
  taken 
  as 
  a 
  measure 
  of 
  the 
  

   intensity. 
  

  

  McGill 
  University, 
  

   Montreal. 
  

  

  o 
  

  

  XL 
  111. 
  Notices 
  respecting 
  New 
  Boohs. 
  

  

  Elementary 
  Practical 
  Mathematics. 
  By 
  Prof. 
  John 
  Perky, 
  E.K.S. 
  

   Pp. 
  xiv 
  + 
  335. 
  6s. 
  Macmillan 
  & 
  Co. 
  Ltd. 
  1913. 
  

  

  NE 
  of 
  the 
  greatest 
  difficulties 
  in 
  teaching 
  mathematics 
  so 
  as 
  to 
  

   make 
  the 
  work 
  interesting 
  to 
  the 
  average 
  student 
  is 
  that 
  it 
  is 
  

   almost 
  impossible 
  to 
  illustrate 
  the 
  work 
  by 
  examples 
  drawn 
  from 
  

   real 
  life. 
  Most 
  of 
  the 
  examples 
  in 
  text-boots 
  are 
  of 
  no 
  intrinsic 
  

   value 
  and 
  are 
  highly 
  artificial. 
  

  

  Professor 
  Perry's 
  book 
  will 
  be 
  welcomed 
  for 
  its 
  great 
  wealth 
  of 
  

   practical 
  examples. 
  They 
  are 
  in 
  most 
  cases 
  too 
  difficult 
  for 
  any 
  

   but 
  advanced 
  students, 
  and 
  we 
  are 
  still 
  in 
  need 
  of 
  elementary 
  

   practical 
  examples. 
  Mr. 
  David 
  Mair 
  has 
  brought 
  out 
  two 
  such 
  

   books, 
  mostly 
  dealing 
  with 
  geometry, 
  and 
  I 
  understand 
  that 
  

   Dr. 
  Nunn 
  is 
  engaged 
  in 
  a 
  book 
  of 
  a 
  similar 
  type 
  dealing 
  chiefly 
  

   with 
  arithmetic 
  and 
  algebra, 
  so 
  that 
  in 
  the 
  near 
  future 
  we 
  shall 
  be 
  

   fairly 
  well 
  supplied. 
  "What 
  will 
  then 
  be 
  needed 
  will 
  be 
  that 
  

   Examining 
  bodies 
  will 
  aim 
  • 
  at 
  making 
  at 
  least 
  some 
  of 
  their 
  

   questions 
  of 
  the 
  practical 
  type, 
  and 
  extending 
  or 
  modifying 
  their 
  

   syllabus 
  of 
  requirements 
  accordingly. 
  

  

  At 
  the 
  same 
  time 
  Prof. 
  Perry 
  seems 
  to 
  me 
  to 
  be 
  too 
  severe 
  in 
  

   his 
  condemnation 
  of 
  what 
  he 
  calls 
  ' 
  academic 
  ' 
  work. 
  A 
  student 
  

   who 
  is 
  brought 
  up 
  entirely 
  on 
  practical 
  problems 
  will 
  not 
  be 
  nearly 
  

   so 
  well 
  equipped 
  for 
  tackling 
  new 
  work 
  as 
  one 
  who 
  has 
  been 
  

   trained 
  on 
  the 
  old 
  carefully 
  graduated 
  theoretic 
  lines 
  — 
  his 
  

   knowledge 
  is 
  likely 
  to 
  be 
  scrappy 
  and 
  slip-shod, 
  though 
  he 
  will 
  

   have 
  learned 
  the 
  habit 
  of 
  making 
  the 
  most 
  of 
  such 
  methods 
  as 
  

   he 
  knows, 
  and 
  have 
  discovered 
  that 
  many 
  difficult 
  problems 
  can 
  be 
  

   made 
  to 
  yield 
  to 
  very 
  simple 
  methods. 
  

  

  It 
  is 
  really 
  for 
  the 
  student 
  with 
  no 
  special 
  aptitude 
  for 
  

   mathematical 
  reasoning 
  that 
  the 
  stimulus 
  of 
  practical 
  examples 
  is 
  

   most 
  needed. 
  To 
  the 
  more 
  thorough 
  student 
  they 
  are 
  only 
  useful 
  

  

  