﻿380 
  Scientific 
  Intelligence. 
  

  

  shown 
  long 
  ago 
  by 
  Stokes 
  that, 
  when 
  a 
  solid 
  body 
  is 
  in 
  motion 
  

   in 
  a 
  frictionless 
  fluid 
  of 
  infinite 
  extent, 
  the 
  effect 
  of 
  the 
  fluid 
  

   pressure 
  is 
  equivalent 
  to 
  an 
  increase 
  in 
  the 
  apparent 
  inertia 
  of 
  

   the 
  body. 
  In 
  the 
  special 
  case 
  of 
  a 
  sphere 
  this 
  increase 
  is 
  theo- 
  

   retically 
  equal 
  to 
  one-half 
  of 
  the 
  mass 
  of 
  the 
  fluid 
  displaced.. 
  

   Accordingly 
  some 
  interest 
  attaches 
  to 
  Cook's 
  investigation 
  from 
  

   the 
  theoretical, 
  as 
  well 
  as 
  from 
  the 
  practical, 
  point 
  of 
  view. 
  

  

  The 
  fluid 
  used 
  was 
  water 
  and 
  it 
  was 
  contained 
  in 
  a 
  cylindrical 
  

   tank 
  15 
  feet 
  in 
  diameter 
  and 
  30 
  feet 
  in 
  depth. 
  The 
  spherical 
  

   body 
  consisted 
  of 
  a 
  mine-case 
  38-2 
  ins. 
  in 
  diameter, 
  having 
  a 
  

   displacement 
  of 
  1080 
  lbs., 
  and 
  being 
  so 
  ballasted 
  as 
  to 
  weigh 
  

   hydrostatically 
  approximately 
  one 
  pound. 
  A 
  light 
  cord 
  ran 
  

   from 
  the 
  mine-case 
  around 
  the 
  drum 
  of 
  a 
  specially-designed 
  

   chronographic 
  instrument 
  that 
  produced 
  a 
  graphical 
  record 
  

   from 
  which 
  simultaneous 
  values 
  of 
  the 
  speed 
  and 
  acceleration 
  

   of 
  the 
  descending 
  body 
  could 
  be 
  readily 
  calculated. 
  

  

  When 
  the 
  acceleration 
  was 
  plotted 
  as 
  ordinate 
  against 
  the 
  

   square 
  of 
  the 
  speed 
  as 
  abscissa 
  it 
  was 
  found 
  that 
  the 
  points 
  

   could 
  be 
  represented, 
  — 
  within 
  the 
  limits 
  of 
  accuracy 
  of 
  the 
  ex- 
  

   perimental 
  data, 
  — 
  by 
  the 
  following 
  linear 
  relation 
  

  

  -^ 
  = 
  0-0193-0-0494 
  v\ 
  

   at 
  

  

  Comparing 
  this 
  empirical 
  equation 
  with 
  the 
  more 
  general 
  for- 
  

   mula 
  

  

  dv 
  _ 
  F 
  Jcv 
  n 
  

  

  and 
  being 
  given 
  that 
  F 
  = 
  0-950 
  X 
  32-18 
  poundals, 
  it 
  is 
  clear 
  

   that 
  n 
  = 
  2 
  and 
  M' 
  = 
  1584 
  lbs. 
  Hence, 
  the 
  effective 
  inertia 
  W 
  

   is 
  1-47 
  times 
  the 
  displacement 
  of 
  the 
  spherical 
  body. 
  Under 
  the* 
  

   experimental 
  conditions, 
  which 
  did 
  not 
  conform 
  in 
  all 
  respects. 
  

   to 
  the 
  analytical 
  hypotheses, 
  the 
  agreement 
  between 
  1-47 
  and 
  

   the 
  theoretical 
  value 
  150 
  may 
  be 
  considered 
  as 
  quite 
  satisfactory. 
  

   Incidentally, 
  on 
  the 
  assumption 
  that 
  the 
  resistance 
  B 
  is 
  propor- 
  

   tional 
  to 
  the 
  square 
  of 
  the 
  diameter 
  of 
  the 
  sphere, 
  that 
  is, 
  B 
  = 
  

   k'd 
  2 
  v 
  2 
  the 
  value 
  of 
  k' 
  was 
  calculated 
  to 
  be 
  0-241 
  ft. 
  lb. 
  sec. 
  

   units.— 
  Phil. 
  Mag., 
  39, 
  350, 
  1920. 
  h. 
  s. 
  u. 
  

  

  7. 
  Osservazioni 
  e 
  Bicerche 
  Sperimentali 
  sidle 
  Scintille 
  Con- 
  

   tinue; 
  by 
  Lavoro 
  Amaduzzi. 
  Pp. 
  61, 
  12 
  figures, 
  2 
  plates. 
  

   Bologna, 
  1919 
  (Nicola 
  Zanichelli). 
  — 
  The 
  material 
  of 
  this 
  mono- 
  

   graph 
  is 
  conveniently 
  divided 
  into 
  three 
  chapters. 
  The 
  first 
  

   chapter 
  is 
  largely 
  introductory 
  and 
  it 
  contains 
  a 
  review 
  of 
  

   Hemsalech's 
  and 
  of 
  Righi's 
  classifications 
  of 
  electric 
  sparks, 
  a 
  

   description 
  of 
  the 
  type 
  of 
  apparatus 
  suitable 
  for 
  the 
  production 
  

   of 
  the 
  four 
  kinds 
  of 
  sparks, 
  and 
  a 
  brief 
  account 
  of 
  the 
  present 
  

   status 
  of 
  the 
  problem. 
  This 
  part 
  of 
  the 
  text 
  is 
  illustrated 
  by 
  a 
  

   full-page 
  plate 
  presenting 
  fourteen 
  colored 
  figures 
  of 
  electrical 
  

   discharges. 
  

  

  