﻿332 
  , 
  Scientific 
  Intelligence. 
  

  

  A 
  certain 
  box, 
  fitted 
  with 
  9 
  plugs, 
  was 
  tested 
  10 
  times, 
  by 
  

   Carey 
  Foster's 
  method, 
  under 
  each 
  of 
  the 
  following 
  conditions, 
  

   the 
  plugs 
  being 
  removed 
  between 
  the 
  tests 
  : 
  (a) 
  plugs 
  in 
  a 
  bath 
  

   of 
  Geryk 
  pump 
  oil, 
  (b) 
  plugs 
  smeared 
  with 
  Geryk 
  pump 
  oil, 
  

   (c) 
  plugs 
  smeared 
  with 
  medicinal 
  paraffin 
  oil, 
  (d) 
  plugs 
  smeared 
  

   with 
  " 
  pure 
  " 
  vaseline, 
  and 
  (e) 
  plugs 
  and 
  lugs 
  clean 
  and 
  unlubri- 
  

   cated. 
  The 
  mean 
  contact 
  resistances 
  were 
  found 
  to 
  be 
  respec- 
  

   tively 
  0-00135, 
  0-00118, 
  0-00124, 
  0-00116, 
  and 
  0*00119 
  ohms. 
  The 
  

   corresponding 
  extreme 
  variations 
  from 
  these 
  means 
  are 
  given 
  as 
  

   ±20, 
  ±18-6, 
  ±19-3, 
  ±8-6, 
  and 
  ± 
  72'2 
  percent. 
  Similar 
  

   results 
  were 
  obtained 
  with 
  three 
  other 
  boxes 
  having 
  17 
  plugs 
  

   each, 
  and 
  with 
  a 
  box 
  of 
  4 
  dials. 
  The 
  conclusions 
  are 
  that 
  the 
  

   usual 
  process 
  of 
  cleaning 
  the 
  surfaces 
  of 
  contact 
  with 
  emery- 
  

   paper 
  or 
  otherwise 
  and 
  using 
  the 
  plugs 
  dry 
  is 
  very 
  unsatisfactory, 
  

   and 
  that 
  the 
  scheme 
  of 
  smearing 
  the 
  plugs 
  with 
  pure 
  vaseline 
  is 
  

   the 
  most 
  convenient 
  and 
  reliable 
  procedure 
  to 
  follow. 
  — 
  Phil. 
  Mag., 
  

   xxxiii, 
  p. 
  211, 
  February, 
  191*7. 
  h. 
  s. 
  u. 
  

  

  8. 
  Unipolar 
  Induction. 
  — 
  The 
  work 
  of 
  E. 
  H. 
  Kennard 
  should 
  

   be 
  added 
  to 
  the 
  list 
  of 
  investigations 
  which 
  have 
  dealt 
  with 
  the 
  

   vexed 
  problem 
  of 
  unipolar 
  induction 
  and 
  its 
  bearing 
  on 
  the 
  mov- 
  

   ing-line 
  hypothesis, 
  on 
  the 
  existence 
  and 
  state 
  of 
  the 
  luminiferous 
  

   ether, 
  etc. 
  For 
  lack 
  of 
  space, 
  a 
  description 
  of 
  the 
  apparatus 
  

   used 
  and 
  an 
  outline 
  of 
  the 
  associated 
  theory 
  will 
  be 
  omitted. 
  By 
  

   rotating 
  a 
  cylindrical 
  condenser 
  inside 
  a 
  magnetized 
  coaxial 
  sole- 
  

   noid 
  it 
  was 
  found 
  that 
  the 
  condenser 
  became 
  charged 
  in 
  accord- 
  

   ance 
  with 
  the 
  theory 
  of 
  Lorentz. 
  Rotation 
  of 
  the 
  solenoid 
  alone 
  

   had 
  no 
  effect, 
  as 
  had 
  previously 
  been 
  observed 
  by 
  Barnett. 
  The 
  

   author 
  also 
  says: 
  "The 
  disproof 
  of 
  the 
  moving-line 
  theory 
  is 
  

   thus 
  completed 
  ; 
  electromagnetic 
  induction 
  depends 
  in 
  part 
  upon 
  

   absolute 
  rotation 
  in 
  the 
  mechanical 
  sense. 
  Analysis 
  in 
  terms 
  of 
  

   electrons 
  seems 
  to 
  make 
  necessary 
  the 
  existence 
  of 
  a 
  stationary 
  

   aether 
  in 
  order 
  to 
  explain 
  the 
  observed 
  effect; 
  so 
  that 
  the 
  phe- 
  

   nomenon 
  seems 
  to 
  present 
  difficulties 
  for 
  those 
  relativists 
  who 
  

   reject 
  the 
  aether." 
  

  

  The 
  following 
  by-product 
  of 
  the 
  work 
  merits 
  attention 
  for 
  

   pedagogical 
  reasons. 
  Some 
  text-books 
  state 
  that 
  the 
  effect 
  of 
  

   rotating 
  the 
  armature 
  of 
  a 
  dynamo 
  is 
  the 
  same 
  as 
  that 
  of 
  rotating 
  

   the 
  field 
  magnets 
  in 
  the 
  opposite 
  direction. 
  This 
  statement 
  must 
  

   be 
  understood 
  to 
  refer 
  to 
  the 
  total 
  electromotive 
  force 
  produced. 
  

   On 
  the 
  other 
  hand, 
  the 
  electromotive 
  force 
  in 
  the 
  first 
  case 
  is 
  

   developed 
  almost 
  entirely 
  in 
  the 
  longitudinal 
  parts 
  of 
  the 
  drum 
  

   winding, 
  while 
  in 
  the 
  second 
  case 
  a 
  large 
  fraction 
  of 
  it 
  is 
  pro- 
  

   duced 
  in 
  the 
  radial 
  parts, 
  and 
  the 
  distribution 
  of 
  electrification 
  

   on 
  the 
  armature 
  will 
  be 
  different 
  in 
  the 
  two 
  cases. 
  — 
  Phil. 
  Mag., 
  

   xxxiii, 
  p. 
  179, 
  February, 
  1917. 
  h. 
  s. 
  u. 
  

  

  9. 
  Model 
  Drawing 
  ; 
  by 
  C. 
  Octavius 
  Wright 
  and 
  W. 
  

   Arthur 
  Rudd. 
  Pp. 
  xviii, 
  246 
  ; 
  300 
  figures. 
  Cambridge, 
  1916 
  

   (University 
  Press 
  and 
  G. 
  P. 
  Putnam's 
  Sons).— 
  The 
  authors 
  have 
  

   found 
  that 
  students 
  become 
  much 
  more 
  proficient 
  in 
  the 
  art 
  of 
  

   model 
  drawing 
  when 
  the 
  usual 
  apparatus 
  of 
  simple 
  geometrical 
  

  

  