﻿746 
  Prof. 
  McLennan 
  and 
  Mr. 
  McLeod 
  : 
  Measurements 
  on 
  

  

  The 
  readings 
  taken 
  on 
  the 
  second 
  voyage 
  it 
  will 
  be 
  seen 
  

   started 
  at 
  5*57 
  ions 
  per 
  c.c. 
  per 
  sec. 
  and 
  finally 
  dropped 
  to 
  

   about 
  4*35, 
  which 
  is 
  the 
  mean 
  of 
  the 
  readings 
  taken 
  on 
  the 
  

   last 
  three 
  days. 
  The 
  high 
  initial 
  readings 
  were 
  probably 
  

   due 
  to 
  radio-active 
  deposits 
  which 
  settled 
  on 
  the 
  ship 
  when 
  

   in 
  port 
  at 
  Montreal, 
  but 
  it 
  is 
  interesting 
  in 
  this 
  connexion 
  

   to 
  note 
  that 
  no 
  important 
  drop 
  was 
  observed 
  in 
  the 
  ionization 
  

   when 
  the 
  steamer 
  left 
  port 
  in 
  the 
  first 
  voyage. 
  If 
  the 
  pre- 
  

   vailing 
  winds 
  at 
  Glasgow 
  were 
  south-west 
  ones 
  it 
  might 
  

   afford 
  an 
  explanation, 
  in 
  part 
  at 
  least, 
  of 
  this 
  result. 
  

  

  It 
  is 
  interesting 
  also 
  to 
  note 
  that 
  the 
  final 
  readings 
  on 
  the 
  

   ss. 
  ' 
  Megantic 
  ' 
  were 
  practically 
  the 
  same 
  as 
  those 
  taken 
  

   during 
  the 
  voyage 
  of 
  the 
  ' 
  Hesperian.' 
  This 
  would 
  go 
  to 
  

   show 
  that 
  the 
  contribution 
  to 
  the 
  ionization 
  by 
  radiation 
  

   from 
  the 
  materials 
  and 
  contents 
  of 
  the 
  steamer 
  was 
  practi- 
  

   cally 
  the 
  same 
  for 
  both 
  ships. 
  Further, 
  as 
  Simpson 
  and 
  

   Wright* 
  had 
  previously 
  obtained 
  4*1 
  ions 
  per 
  c.c. 
  per 
  sec. 
  

   for 
  the 
  ionization 
  in 
  a 
  closed 
  zinc 
  vessel 
  on 
  a 
  small 
  skiff 
  on 
  

   the 
  Atlantic, 
  this 
  would 
  go 
  to 
  show 
  that 
  the 
  amount 
  con- 
  

   tributed 
  to 
  the 
  ionization 
  by 
  radiation 
  from 
  the 
  ship 
  was 
  

   inconsiderable. 
  

  

  The 
  mean 
  of 
  the 
  readings 
  taken 
  on 
  the 
  ocean 
  with 
  the 
  

   Wulf 
  electrometer, 
  viz. 
  4*33 
  ions 
  per 
  c.c. 
  per 
  sec, 
  it 
  will 
  be 
  

   seen 
  was 
  1*7 
  ions 
  per 
  c.c. 
  per 
  sec. 
  less 
  than 
  the 
  mean 
  of 
  the 
  

   readings 
  previously 
  taken 
  with 
  the 
  Wilson 
  electrometer, 
  and 
  

   in 
  view 
  of 
  the 
  accuracy 
  and 
  ease 
  with 
  which 
  the 
  readings 
  

   could 
  be 
  made 
  with 
  the 
  Wulf 
  instrument, 
  the 
  value 
  4*33 
  ions 
  

   may 
  be 
  accepted 
  as 
  closely 
  representing 
  the 
  true 
  value 
  of 
  the 
  

   ionization 
  obtainable 
  on 
  a 
  large 
  ship 
  on 
  the 
  sea. 
  

  

  IV. 
  Measurements 
  on 
  Land. 
  

  

  At 
  various 
  times 
  previous 
  to 
  and 
  succeeding 
  the 
  two 
  

   voyages, 
  as 
  well 
  as 
  at 
  times 
  in 
  the 
  intervals 
  between 
  them, 
  

   readings 
  were 
  taken 
  with 
  the 
  instrument 
  at 
  a 
  number 
  of 
  

   points 
  at 
  or 
  near 
  Toronto 
  and 
  also 
  at 
  a 
  number 
  of 
  places 
  on 
  

   the 
  other 
  side 
  of 
  the 
  Atlantic. 
  These 
  are 
  summarized 
  in 
  

   Table 
  III., 
  and 
  along 
  with 
  them 
  are 
  given 
  the 
  readings 
  

   taken 
  at 
  a 
  number 
  of 
  places 
  with 
  the 
  Wilson 
  Compensating 
  

   Gold-leaf 
  Electrometer. 
  

  

  From 
  the 
  numbers 
  given 
  it 
  will 
  be 
  seen 
  that 
  the 
  readings 
  

   with 
  both 
  instruments 
  were 
  practically 
  the 
  same 
  at 
  Mid- 
  

   lothian, 
  Scotland, 
  at 
  Cambridge, 
  England, 
  and 
  at 
  the 
  

   Physical 
  Laboratory, 
  Toronto. 
  This, 
  combined 
  with 
  the 
  

  

  * 
  Simpson 
  and 
  Wright, 
  Proc. 
  Rov. 
  Soc. 
  Ser. 
  A. 
  vol. 
  lxxxv. 
  p. 
  175 
  

   (1911). 
  

  

  