﻿296 
  Scientific 
  Intelligence. 
  

  

  reached 
  that 
  it 
  does 
  not 
  possess 
  the 
  qualities 
  required 
  of 
  a 
  pri- 
  

   mary 
  standard, 
  although 
  under 
  certain 
  conditions 
  it 
  may 
  be 
  of 
  

   great 
  value 
  as 
  a 
  standard 
  of 
  reference. 
  

  

  Passing 
  to 
  the 
  subject 
  of 
  the 
  molten 
  platinum 
  standard, 
  first 
  

   proposed 
  by 
  J. 
  Violle 
  in 
  1881, 
  the 
  author 
  concludes, 
  after 
  experi- 
  

   menting 
  upon 
  the 
  fusion 
  of 
  platinum 
  by 
  an 
  electric 
  current 
  and 
  

   with 
  the 
  oxyhydrogen 
  blowpipe, 
  that 
  the 
  latter 
  leads 
  to 
  the 
  

   best 
  results 
  if 
  the 
  platinum 
  selected 
  is 
  chemically 
  pure, 
  the 
  cruci- 
  

   ble 
  is 
  made 
  of 
  pure 
  lime, 
  the 
  hydrogen 
  contains 
  no 
  hydrocarbons, 
  

   and 
  the 
  gases 
  are 
  burnt 
  in 
  the 
  ratio 
  of 
  four 
  volumes 
  of 
  hydrogen 
  

   to 
  three 
  of 
  oxygen. 
  The 
  temperature 
  of 
  the 
  flame, 
  if 
  the 
  last 
  

   condition 
  is 
  observed, 
  is 
  but 
  little 
  above 
  the 
  melting 
  point 
  of 
  

   platinum, 
  and 
  the 
  metal 
  is 
  not 
  essentially 
  superheated. 
  A 
  

   detailed 
  account 
  is 
  given 
  of 
  the 
  methods 
  employed 
  for 
  attaining 
  

   a 
  high 
  degree 
  of 
  accuracy, 
  particularly 
  in 
  the 
  photometric 
  parts 
  

   of 
  the 
  work, 
  and 
  a 
  series 
  of 
  tables 
  show 
  the 
  results 
  reached; 
  for 
  

   details 
  of 
  these 
  reference 
  must 
  be 
  made 
  to 
  the 
  original 
  paper. 
  

  

  The 
  final 
  conclusion 
  is 
  important, 
  viz., 
  that 
  under 
  standard 
  

   conditions 
  the 
  probable 
  variation 
  in 
  the 
  light 
  emitted 
  by 
  molten 
  

   platinum 
  is 
  not 
  above 
  1 
  per 
  cent, 
  and 
  with 
  more 
  perfect 
  apparatus 
  

   and 
  somewhat 
  better 
  experimental 
  conditions, 
  the 
  accuracy 
  could 
  

   be 
  increased 
  beyond 
  this 
  point. 
  It 
  is 
  not 
  impossible, 
  even, 
  that 
  

   the 
  accuracy 
  of" 
  the 
  platinum 
  standard 
  may 
  attain 
  to, 
  or 
  even 
  

   surpass, 
  the 
  limit 
  fixed 
  by 
  physiological 
  conditions. 
  — 
  Proc. 
  Roy. 
  

   Soc, 
  lxv, 
  pp. 
  469-503. 
  

  

  10. 
  A 
  Text-Book 
  of 
  Physics 
  ; 
  by 
  W. 
  Watson, 
  Assist. 
  Professor 
  

   of 
  Physics 
  at 
  the 
  Royal 
  College 
  of 
  Science, 
  London. 
  Pp. 
  xxii, 
  

   896. 
  London 
  1899 
  (Longmans, 
  Green 
  & 
  Co.). 
  — 
  The 
  varied 
  wants 
  

   of 
  different 
  teachers 
  of 
  Physics 
  have 
  led 
  to 
  the 
  publication 
  of 
  a 
  

   long 
  series 
  of 
  text-books, 
  many 
  of 
  them 
  of 
  a 
  high 
  degree 
  of 
  

   excellence, 
  though 
  no 
  two 
  cover 
  just 
  the 
  same 
  field. 
  Of 
  this 
  

   latest 
  addition 
  to 
  the 
  series 
  it 
  is 
  possible 
  to 
  speak 
  in 
  terms 
  of 
  

   decided 
  commendation. 
  Many 
  teachers, 
  among 
  those 
  who 
  have 
  

   not 
  written 
  book 
  for 
  their 
  own 
  classes, 
  are 
  likely 
  to 
  find 
  that 
  it 
  

   more 
  nearly 
  fills 
  their 
  wants 
  than 
  any 
  one 
  of 
  its 
  predecessors. 
  

   It 
  gives 
  a 
  clear, 
  systematic 
  and 
  thorough 
  presentation 
  of 
  the 
  

   whole 
  subject 
  and 
  from 
  a 
  rather 
  advanced 
  standpoint, 
  though 
  

   it 
  does 
  not 
  assume 
  the 
  knowledge 
  of 
  more 
  than 
  the 
  ordinary 
  

   methods 
  of 
  mathematics. 
  

  

  The 
  book 
  is 
  not 
  an 
  easy 
  one 
  for 
  a 
  large 
  class 
  of 
  elementary 
  

   students, 
  certain 
  portions, 
  for 
  instance 
  the 
  chapters 
  on 
  electricity, 
  

   being 
  rather 
  difficult, 
  — 
  more 
  so 
  in 
  fact 
  than 
  those 
  on 
  light, 
  where 
  

   the 
  methods 
  of 
  geometrical 
  optics 
  are 
  pretty 
  closely 
  adhered 
  to. 
  

   In 
  the 
  former 
  case, 
  the 
  author 
  seems 
  to 
  go 
  almost 
  too 
  far 
  in 
  his 
  

   admirable 
  plan 
  not 
  to 
  dwell 
  too 
  much 
  upon 
  the 
  experimental 
  side 
  

   of 
  the 
  subject. 
  Some 
  students 
  will 
  wish 
  that 
  the 
  printer 
  had 
  

   been 
  a 
  little 
  more 
  liberal 
  in 
  the 
  use 
  of 
  italics, 
  as 
  it 
  is 
  a 
  help 
  to 
  

   one 
  approaching 
  the 
  subject 
  for 
  the 
  first 
  time 
  to 
  have 
  the 
  essen- 
  

   tial 
  subjects 
  and 
  principles 
  discussed 
  brought 
  at 
  once 
  clearly 
  

   before 
  the 
  eye. 
  It 
  is 
  also 
  rather 
  to 
  be 
  regretted 
  that 
  the 
  pub- 
  

  

  