﻿Chemistry 
  and 
  Physics. 
  485 
  

  

  9. 
  Use 
  of 
  rapid 
  electrical 
  oscillations 
  for 
  determining 
  dielectric 
  

   constants. 
  — 
  W. 
  Nkrnst 
  describes 
  a 
  modification 
  of 
  his 
  well- 
  

   known 
  bridge 
  for 
  determining 
  dielectric 
  constants. 
  It 
  is 
  a 
  spe- 
  

   cies 
  of 
  double 
  transformer. 
  A 
  spark 
  gap 
  is 
  placed 
  in 
  the 
  pri- 
  

   mary 
  of 
  one 
  transformer. 
  ' 
  The 
  bridge 
  combination 
  is 
  connected 
  

   to 
  the 
  terminals 
  of 
  the 
  secondary 
  of 
  this 
  transformer. 
  In 
  place 
  

   of 
  a 
  telephone 
  there 
  is 
  substituted 
  the 
  primary 
  of 
  the 
  second 
  

   transformer 
  and 
  a 
  spark 
  gap 
  is 
  placed 
  in 
  the 
  secondary 
  of 
  the 
  

   latter 
  transformer. 
  The 
  extinction 
  of 
  the 
  spark 
  in 
  this 
  secondary 
  

   denotes 
  a 
  balance. 
  The 
  apparatus 
  is 
  suitable 
  for 
  the 
  measure 
  of 
  

   the 
  dielectric 
  constants 
  of 
  conducting 
  fluids. 
  Electrolytic 
  

   resistances 
  can 
  also 
  be 
  determined 
  to 
  the 
  fraction 
  of 
  one 
  per 
  

   cent; 
  disturbances 
  from 
  polarization 
  do 
  not 
  enter. 
  — 
  Wied. 
  Ann., 
  

   No. 
  4, 
  1897, 
  pp. 
  600-624. 
  J. 
  t. 
  

  

  10. 
  Ultra-red 
  rays. 
  — 
  H. 
  Rubens 
  and 
  A. 
  Trowbridge 
  reach 
  the 
  

   conclusion 
  that 
  it 
  is 
  possible 
  by 
  means 
  of 
  a 
  double 
  spectral 
  sepa- 
  

   ration 
  by 
  the 
  help 
  of 
  two 
  acute 
  angled 
  prisms 
  of 
  rock 
  salt 
  to 
  

   detect 
  the 
  energy 
  of 
  the 
  spectrum 
  as 
  far 
  as 
  18/x, 
  and 
  that 
  with 
  

   the 
  aid 
  of 
  sylvine 
  prisms 
  it 
  is 
  possible 
  to 
  extend 
  this 
  limit 
  to 
  23/x. 
  

   — 
  Wied. 
  Ann., 
  No. 
  4, 
  1897, 
  pp. 
  724-739. 
  J. 
  t. 
  

  

  11. 
  Production 
  of 
  X-rays 
  of 
  different 
  penetrative 
  values. 
  — 
  Mr. 
  

   A. 
  A. 
  C. 
  Swinton 
  states 
  that 
  the 
  penetrative 
  value 
  of 
  the 
  X-rays 
  

   increases 
  with 
  the 
  degree 
  of 
  vacuum 
  in 
  which 
  they 
  are 
  produced. 
  

   At 
  a 
  certain 
  vacuum 
  the 
  bones 
  of 
  the 
  hand, 
  for 
  instance, 
  are 
  

   clearly 
  seen 
  ; 
  with 
  a 
  higher 
  vacuum 
  the 
  flesh 
  becomes 
  very 
  trans- 
  

   parent, 
  while 
  the 
  bones 
  are 
  still 
  opaque. 
  At 
  a 
  still 
  higher 
  vacuum 
  

   the 
  bones 
  become 
  nearly 
  as 
  transparent 
  as 
  the 
  flesh 
  ; 
  and 
  finally, 
  

   at 
  the 
  highest 
  vacuum 
  the 
  whole 
  hand 
  shows 
  only 
  a 
  faint 
  shadow 
  

   on 
  the 
  fluorescent 
  screen. 
  Similar 
  effects 
  can 
  be 
  produced 
  with 
  a 
  

   constant 
  vacuum 
  by 
  varying 
  the 
  power 
  of 
  the 
  Ruhmkorf 
  coil 
  or 
  

   by 
  altering 
  the 
  distance 
  between 
  the 
  cathode 
  and 
  the 
  anti- 
  

   cathodes. 
  On 
  the 
  assumption 
  that 
  cathode 
  rays 
  consist 
  of 
  

   regularly 
  charged 
  molecules 
  which 
  are 
  repelled 
  from 
  the 
  similarly 
  

   electrified 
  cathode, 
  with 
  an 
  initial 
  velocity 
  that 
  depends 
  upon 
  the 
  

   degree 
  of 
  electrical 
  excitation 
  of 
  the 
  cathode, 
  the 
  conditions 
  which 
  

   produce 
  X-rays 
  of 
  high 
  penetrative 
  value 
  are 
  those 
  which 
  would 
  

   conduce 
  to 
  a 
  high 
  average 
  velocity 
  of 
  the 
  molecules 
  at 
  the 
  

   moment 
  they 
  strike 
  the 
  anti-cathode 
  and 
  to 
  a 
  high 
  average 
  dif- 
  

   ference 
  of 
  potential 
  between 
  the 
  travelling 
  molecules 
  and 
  the 
  anti- 
  

   cathode 
  at 
  the 
  moment 
  of 
  impact. 
  The 
  conditions 
  for 
  X-rays 
  of 
  

   low 
  penetrative 
  power 
  are 
  those 
  which 
  conduce 
  to 
  a 
  lower 
  aver- 
  

   age 
  velocity 
  of 
  the 
  molecules 
  and 
  to 
  a 
  less 
  difference 
  of 
  potential 
  

   between 
  the 
  latter 
  and 
  the 
  anti-cathode. 
  The 
  quantity 
  of 
  X-rays 
  

   is 
  independent 
  of 
  the 
  material 
  of 
  which 
  the 
  anti-cathode 
  surface 
  is 
  

   made 
  : 
  anti-cathodes 
  of 
  aluminum, 
  iron, 
  copper, 
  silver 
  and 
  platinum 
  

   give 
  X-rays 
  of 
  the 
  same 
  penetrative 
  power. 
  — 
  Nature, 
  April 
  29, 
  

   1897, 
  p. 
  621. 
  j. 
  t. 
  

  

  12. 
  Physiological 
  effects 
  of 
  the 
  N-rays. 
  — 
  M. 
  Sorel 
  discusses 
  the 
  

   pathological 
  and 
  physiological 
  effects 
  of 
  the 
  X-rays 
  and 
  believes 
  

   that 
  it 
  is 
  inadvisable 
  to 
  use 
  the 
  rays 
  on 
  portions 
  of 
  the 
  human 
  

  

  