﻿Chemistry 
  and 
  Physics. 
  647 
  

  

  with 
  the 
  wave-length 
  (5572-6) 
  of 
  one 
  of 
  the 
  stronger 
  argon 
  lines. 
  

   The 
  wave-lengths 
  of 
  the 
  prominent 
  heads 
  of 
  the 
  nitrogen 
  band 
  

   spectrum 
  are 
  4708-2, 
  4651-2, 
  4278'0, 
  4236'3, 
  4200*9, 
  and 
  3914-4. 
  

   A 
  comparison 
  of 
  these 
  values 
  with 
  the 
  tigures 
  given 
  above 
  for 
  the 
  

   auroral 
  lines 
  leaves 
  no 
  doubt 
  as 
  to 
  the 
  origin 
  of 
  the 
  radiations 
  in 
  

   question. 
  Moreover 
  a 
  weak 
  comparison 
  photograph 
  of 
  the 
  nega- 
  

   tive 
  glow 
  of 
  nitrogen, 
  taken 
  with 
  the 
  same 
  apparatus, 
  showed 
  

   that 
  the 
  distribution 
  of 
  intensity 
  of 
  the 
  strongest 
  "lines" 
  (4708, 
  

   4278, 
  3914) 
  was 
  the 
  same 
  as 
  in 
  the 
  spectrum 
  of 
  the 
  northern 
  

   lights. 
  Also, 
  the 
  most 
  intense 
  of 
  these 
  auroral 
  lines 
  (4278) 
  shades 
  

   off 
  on 
  the 
  more 
  refrangible 
  side 
  precisely 
  as 
  does 
  the 
  correspond- 
  

   ing 
  nitrogen 
  band. 
  Unfortunately 
  the 
  lines 
  which 
  were 
  of 
  suffi- 
  

   cient 
  intensity 
  to 
  be 
  measured 
  are 
  not 
  numerous 
  enough 
  to 
  decide 
  

   the 
  question 
  as 
  to 
  whether 
  aurorse 
  are 
  caused 
  by 
  electronic 
  rays 
  

   or 
  by 
  rays 
  of 
  the 
  a 
  type. 
  — 
  Physik. 
  Zeitschr., 
  No. 
  15, 
  August 
  1913, 
  

   p. 
  677. 
  h. 
  s. 
  u. 
  

  

  8. 
  To 
  Produce 
  a 
  Continuous 
  Spectrum 
  in 
  the 
  Ultra-violet. 
  — 
  

   Investigators 
  of 
  absorption 
  spectra 
  have 
  long 
  felt 
  the 
  need 
  of 
  a 
  

   source 
  of 
  intense, 
  continuous 
  radiation 
  in 
  the 
  ultra-violet. 
  This 
  

   is 
  especially 
  true 
  in 
  the 
  case 
  of 
  fine 
  absorption 
  lines 
  as 
  given 
  by 
  

   gases 
  and 
  vapors. 
  The 
  sources 
  of 
  continuous 
  ultra-violet 
  light 
  

   hitherto 
  found 
  have 
  had 
  little 
  practical 
  value 
  because 
  of 
  their 
  

   faintness, 
  or 
  of 
  their 
  great 
  inconvenience, 
  etc. 
  It 
  is 
  pointed 
  out 
  

   in 
  a 
  short 
  paper 
  by 
  Victor 
  Henri 
  that 
  if 
  a 
  spark 
  of 
  high 
  fre- 
  

   quency, 
  such 
  as 
  is 
  used 
  in 
  the 
  Tesla 
  and 
  d'Arsonval 
  experiments, 
  

   is 
  employed 
  instead 
  of- 
  the 
  usual 
  condensed 
  spark, 
  excellent 
  results 
  

   can 
  be 
  obtained. 
  The 
  spark 
  gap 
  must 
  be 
  under 
  water 
  and 
  the 
  

   electrodes 
  are 
  preferably 
  made 
  of 
  aluminium. 
  A 
  spark 
  4 
  or 
  5 
  mtrs 
  

   long 
  may 
  be 
  readily 
  produced 
  and 
  it 
  is 
  said 
  to 
  be 
  very 
  constant. 
  

   With 
  an 
  exposure 
  of 
  only 
  30 
  to 
  60 
  sees, 
  the 
  continuous 
  spectrum 
  

   extends 
  to 
  about 
  wave-length 
  2150 
  A. 
  The 
  spectrogram 
  repro- 
  

   duced 
  in 
  the 
  plate 
  is 
  unusually 
  good. 
  The 
  continuity 
  of 
  the 
  spec- 
  

   trum 
  is 
  broken 
  in 
  a 
  few 
  places 
  by 
  intense 
  lines 
  and 
  by 
  narrow 
  

   reversals. 
  In 
  general, 
  this 
  lack 
  of 
  perfect 
  continuity 
  would 
  

   not 
  be 
  a 
  practical 
  drawback. 
  — 
  Physik. 
  Zeitschr., 
  No. 
  12, 
  June 
  

   1913, 
  p. 
  516. 
  h. 
  s. 
  u. 
  

  

  .9. 
  The 
  Gyroscope 
  ; 
  by 
  F. 
  J. 
  B. 
  Cordeiro. 
  Pp. 
  vii, 
  105, 
  

   with 
  19 
  figures. 
  New 
  York, 
  1913 
  (Spon 
  and 
  Chamberlain). 
  — 
  The 
  

   justification 
  of 
  the 
  production 
  of 
  a 
  new 
  book 
  on 
  gyroscopic 
  phe- 
  

   nomena 
  is 
  expressed 
  by 
  the 
  author 
  in 
  the 
  following 
  words 
  : 
  " 
  The 
  

   student 
  with 
  an 
  elementary 
  knowledge 
  of 
  mathematics, 
  who 
  

   attempts 
  to 
  understand 
  gyroscopics 
  from 
  a 
  study 
  of 
  its 
  scattered 
  

   parts 
  in 
  standard 
  treatises, 
  and 
  from 
  the 
  few 
  monographs 
  as 
  yet 
  

   written, 
  will 
  find 
  the 
  task 
  tedious 
  — 
  probably 
  repulsive." 
  " 
  For 
  

   this 
  reason, 
  it 
  has 
  seemed 
  advisable 
  to 
  the 
  author 
  to 
  write 
  a 
  mon- 
  

   ograph 
  which 
  may 
  be 
  easily 
  understood 
  by 
  anybody 
  possessing 
  

   an 
  elementary 
  knowledge 
  of 
  mechanics 
  and 
  the 
  calculus." 
  The 
  

   book 
  is 
  divided 
  into 
  two 
  parts 
  which 
  deal 
  respectively 
  with 
  the 
  

   development 
  of 
  the 
  theory 
  from 
  the 
  fundamental 
  gyroscopic 
  

  

  equation 
  C<o6 
  = 
  Aip, 
  and 
  with 
  the 
  practical 
  applications 
  of 
  the 
  

  

  