﻿300 
  MR 
  J. 
  DALMAHOY 
  ON 
  THE 
  WEIGHT 
  OF 
  AQUEOUS 
  VAPOUR 
  

  

  The 
  aqueous 
  vapour 
  was 
  condensed 
  on 
  the 
  inner 
  surface 
  of 
  a 
  nearly 
  cylindrical 
  

   copper 
  vessel, 
  the 
  depth 
  of 
  which 
  was 
  0*5 
  of 
  an 
  inch 
  ; 
  the 
  diameter 
  at 
  the 
  bottom 
  

   3 
  inches, 
  the 
  diameter 
  at 
  the 
  mouth 
  3'075 
  inches 
  ; 
  consequently 
  the 
  inner 
  area 
  

   was 
  equal 
  to 
  11*8 
  square 
  inches. 
  This 
  vessel 
  had 
  a 
  thin 
  copper 
  lid, 
  the 
  catch 
  of 
  

   which 
  adhered 
  to 
  the 
  inner 
  surface, 
  and 
  so 
  did 
  not 
  interfere 
  with 
  the 
  thorough 
  

   removal 
  of 
  moisture 
  from 
  the 
  outer 
  surface. 
  

  

  The 
  temperature 
  of 
  the 
  condensing 
  surface, 
  it 
  has 
  been 
  already 
  remarked, 
  was 
  

   uniformly 
  32° 
  Fahr. 
  This 
  temperature 
  was 
  maintained 
  by 
  filling 
  with 
  pounded 
  

   ice 
  a 
  cylindrical 
  copper 
  box, 
  and 
  burying 
  in 
  it 
  the 
  condensing 
  vessel, 
  all 
  except 
  

   its 
  upper 
  edge, 
  which 
  was 
  made 
  to 
  fit 
  into, 
  and 
  slightly 
  project 
  above, 
  a 
  circular 
  

   opening 
  in 
  the 
  top 
  of 
  the 
  box. 
  

  

  The 
  following 
  are 
  the 
  steps 
  of 
  the 
  process 
  by 
  which 
  the 
  weight 
  of 
  the 
  moisture 
  

   condensed 
  on 
  the 
  cold 
  surface 
  was 
  ascertained. 
  

  

  The 
  condensing 
  vessel 
  and 
  its 
  lid 
  were 
  first 
  carefully 
  dried 
  and 
  then 
  weighed 
  

   in 
  a 
  balance, 
  which 
  was 
  sensible 
  to 
  *01 
  of 
  a 
  grain, 
  when 
  each 
  scale 
  was 
  loaded 
  

   with 
  800 
  grains. 
  The 
  vessel, 
  with 
  its 
  lid 
  closely 
  applied, 
  was 
  now 
  placed 
  among 
  

   ice, 
  as 
  before 
  described, 
  and 
  allowed 
  to 
  cool 
  for 
  about 
  five 
  minutes. 
  The 
  lid 
  was 
  

   then 
  removed, 
  and 
  the 
  condensing 
  surface 
  exposed 
  either 
  to 
  a 
  current 
  of 
  air 
  of 
  

   known 
  velocity, 
  or 
  to 
  calm 
  air. 
  After 
  the 
  exact 
  interval 
  of 
  five 
  minutes 
  the 
  lid 
  

   was 
  replaced, 
  and 
  the 
  vessel 
  was 
  taken 
  out 
  from 
  among 
  the 
  ice 
  ; 
  its 
  temperature 
  

   was 
  then 
  raised 
  above 
  the 
  dew-point 
  by 
  the 
  heat 
  of 
  the 
  hand, 
  while 
  its 
  outer 
  surface 
  

   was 
  carefully 
  dried. 
  Lastly, 
  it 
  was 
  again 
  weighed, 
  and 
  the 
  excess 
  of 
  this 
  above 
  

   the 
  former 
  result 
  was 
  equal 
  to 
  the 
  weight 
  of 
  moisture 
  which 
  had 
  been 
  condensed. 
  

  

  The 
  results 
  thus 
  obtained 
  will 
  be 
  found 
  in 
  Table 
  I., 
  from 
  column 
  twelfth 
  to 
  

   column 
  seventeenth 
  inclusive. 
  

  

  It 
  appears 
  from 
  column 
  twelfth, 
  that 
  when 
  the 
  air 
  was 
  calm, 
  and 
  the 
  mouth 
  

   of 
  the 
  condensing 
  vessel 
  was 
  directed 
  upwards, 
  the 
  quantity 
  of 
  condensed 
  vapour 
  

   was 
  so 
  small 
  and 
  variable 
  as 
  to 
  render 
  it 
  probable 
  that, 
  under 
  this 
  arrangement, 
  

   there 
  would 
  have 
  been 
  no 
  sensible 
  condensation 
  at 
  all, 
  had 
  it 
  not 
  been 
  for 
  those 
  

   irregular 
  currents, 
  which 
  are 
  known 
  to 
  prevail 
  even 
  in 
  air 
  apparently 
  calm. 
  

  

  Column 
  thirteenth 
  shews 
  that 
  when 
  the 
  air 
  was 
  calm, 
  and 
  the 
  mouth 
  of 
  the 
  

   vessel 
  was 
  turned 
  downwards, 
  much 
  more 
  vapour 
  was 
  condensed 
  than 
  when 
  the 
  

   mouth 
  was 
  upwards. 
  This 
  was 
  evidently 
  the 
  effect 
  of 
  a 
  current 
  produced 
  by 
  contact 
  

   of 
  the 
  warm 
  air 
  with 
  the 
  cold 
  condensing 
  surface, 
  and 
  which, 
  for 
  obvious 
  reasons, 
  

   could 
  not 
  take 
  place 
  when 
  the 
  mouth 
  of 
  the 
  vessel 
  was 
  directed 
  upwards. 
  The 
  

   effect 
  of 
  this 
  current 
  on 
  the 
  rate 
  of 
  condensation 
  seemed 
  to 
  vary 
  nearly 
  as 
  t—t"', 
  

   at 
  least 
  it 
  would 
  be 
  difficult, 
  except 
  on 
  this 
  assumption, 
  to 
  reconcile 
  the 
  four 
  last 
  

   with 
  the 
  preceding 
  results 
  in 
  the 
  column. 
  

  

  The 
  last 
  four 
  columns 
  exhibit 
  the 
  results 
  of 
  experiments, 
  in 
  which 
  the 
  con- 
  

   densing 
  surface 
  was 
  exposed 
  to 
  an 
  artificial 
  current 
  of 
  air. 
  

  

  The 
  current 
  was 
  produced 
  by 
  means 
  of 
  a 
  common 
  fire-blower, 
  and 
  the 
  velo- 
  

  

  