﻿f.S2 
  

  

  Prof. 
  J. 
  Joly 
  on 
  the 
  

  

  It 
  will 
  be 
  noticed 
  that 
  in 
  every 
  case 
  the 
  readings 
  of 
  

   Vesuvian 
  lavas 
  from 
  1631 
  to 
  the 
  present 
  day 
  are 
  remarkably 
  

   high 
  ; 
  up 
  to 
  three 
  times 
  the 
  normal 
  for 
  igneous 
  rocks 
  and, 
  

   indeed, 
  even 
  higher. 
  The 
  thorium-content, 
  although 
  large 
  

   in 
  comparison 
  with 
  what 
  generally 
  prevails 
  in 
  the 
  rocks 
  of 
  

   the 
  St. 
  Gothard 
  series 
  (Phil. 
  Mag. 
  July 
  1909) 
  are 
  not 
  con- 
  

   spicuously 
  higher 
  in 
  the 
  Vesuvian 
  rocks 
  than 
  in 
  the 
  rocks 
  

   from 
  other 
  volcanoes. 
  The 
  highest 
  reading 
  was 
  obtained 
  

   for 
  the 
  Krakatao 
  pumice. 
  

  

  The 
  Vesuvian 
  lavas 
  appear 
  to 
  show 
  a 
  progressive 
  increase 
  

   of 
  radioactivity 
  according 
  as 
  they 
  are 
  of 
  more 
  recent 
  eruption. 
  

   The 
  old 
  leucitic 
  rock 
  of 
  Monte 
  Somma 
  is 
  of 
  special 
  interest. 
  

   According 
  to 
  this 
  one 
  sample 
  of 
  the 
  earlier 
  rocks 
  the 
  radio- 
  

   activity 
  was 
  at 
  first 
  actually 
  less 
  than 
  normal. 
  The 
  culmin- 
  

   ating 
  richness 
  in 
  radium 
  is 
  attained 
  in 
  a 
  sample 
  from 
  the 
  

   interior 
  of 
  the 
  lava-flow 
  of 
  April 
  1906. 
  (The 
  '* 
  ejected 
  old 
  

   lava 
  block 
  ^■' 
  in 
  the 
  list 
  is, 
  of 
  course, 
  not 
  truly 
  of 
  this 
  date.) 
  

   Unless 
  w^e 
  conclude 
  that 
  the 
  radium 
  is 
  transforming 
  within 
  

   these 
  lavas 
  after 
  their 
  ejection 
  at 
  a 
  rate 
  much 
  greater 
  than 
  

   would 
  be 
  expected 
  from 
  the 
  period 
  inferred 
  on 
  experimental 
  

   grounds, 
  and 
  that 
  the 
  loss 
  is 
  not 
  being 
  made 
  good, 
  we 
  must 
  

   assume 
  that 
  as 
  time 
  progresses, 
  this 
  volcano 
  is 
  tapping 
  

   materials 
  richer 
  and 
  richer 
  in 
  radium. 
  There 
  is 
  no 
  impro- 
  

   bability 
  in 
  this 
  explanation 
  save 
  what 
  is 
  involved 
  in 
  the 
  

   rather 
  contradictory 
  fact 
  that 
  the 
  lavas 
  of 
  Vesuvius 
  have 
  

   shown 
  a 
  remarkable 
  constancy 
  in 
  chemical 
  composition 
  from 
  

   the 
  earliest 
  times. 
  This 
  is 
  noticed 
  by 
  many 
  authorities, 
  but 
  

   specially 
  by 
  Rosenbusch 
  ("Elemente 
  der 
  Gesteinslehre,' 
  

   p. 
  344), 
  who 
  remarks 
  that 
  notwithstanding 
  great 
  variations 
  

   in 
  texture, 
  colour, 
  and 
  the 
  nature 
  of 
  the 
  phenocrysts, 
  their 
  

   chemical 
  constitution 
  has 
  been 
  extraordinai'ily 
  constant 
  from 
  

   the 
  oldest 
  pre-historic 
  eruptions 
  of 
  Monte 
  Somma 
  to 
  the 
  

   most 
  recent 
  eruptions 
  of 
  Vesuvius. 
  It 
  is 
  therefore 
  surprising 
  

   to 
  find 
  the 
  radium 
  (or 
  uranium) 
  content 
  varying 
  not 
  less 
  

   than 
  five-fold. 
  

  

  The 
  lavas 
  from 
  the 
  surrounding 
  volcanoes 
  emanate 
  from 
  

   distinct 
  petrographical 
  provinces 
  and 
  show 
  the 
  most 
  diverse 
  

   chemical 
  compositions 
  (Bonney, 
  'Volcanoes/ 
  p. 
  207). 
  Their 
  

   failure 
  to 
  show 
  the 
  high 
  radioactivity 
  of 
  the 
  Vesuvian 
  lavas 
  

   is, 
  therefore, 
  not 
  remarkable. 
  On 
  the 
  whole, 
  the 
  Lipari 
  and 
  

   Etna 
  lavas 
  stand 
  high 
  among 
  lavas 
  from 
  other 
  parts 
  of 
  the 
  

   world. 
  But 
  an 
  extension 
  of 
  the 
  number 
  of 
  determinations 
  

   may 
  reveal 
  many 
  cases 
  of 
  radioactivity 
  quite 
  as 
  high. 
  And, 
  

   of 
  course, 
  the 
  same 
  remark 
  may 
  be 
  made 
  in 
  reference 
  to 
  the 
  

   Vesuvian 
  results. 
  

  

  The 
  possibility 
  of 
  a 
  connexion 
  between 
  radioactivity 
  and 
  

  

  