﻿Air-Pressures 
  used 
  in 
  playing 
  Brass 
  Instruments. 
  385 
  

  

  for 
  the 
  wet 
  bulb. 
  It 
  cannot 
  compete 
  in 
  simplicity 
  with 
  the 
  

   wet 
  bulb 
  in 
  its 
  simplest 
  form, 
  but 
  it 
  can 
  compete 
  with 
  the 
  

   various 
  modifications 
  (whirled 
  thermometers, 
  &c). 
  

  

  For 
  the 
  range 
  studied 
  the 
  constant 
  *93 
  can 
  be 
  used 
  for 
  k, 
  

   and 
  it 
  is 
  hoped 
  that 
  this 
  will 
  be 
  tested 
  for 
  other 
  climates 
  and 
  

   below 
  the 
  freezing-point. 
  A 
  small 
  error 
  in 
  k 
  is 
  of 
  very 
  little 
  

   importance, 
  owing 
  to 
  the 
  small 
  value 
  of 
  t 
  — 
  6. 
  

  

  (7) 
  Conclusion. 
  — 
  The 
  method 
  has 
  been 
  shown 
  simple; 
  the 
  

   elementary 
  theory 
  is 
  thought 
  rigorous 
  ; 
  the 
  extension 
  to 
  

   small 
  thermal 
  effects 
  is 
  justified 
  in 
  numerous 
  experiments 
  ; 
  

   k 
  has 
  turned 
  out 
  to 
  be 
  very 
  nearly 
  -93 
  over 
  as 
  wide 
  a 
  range 
  

   as 
  was 
  open 
  to 
  study 
  ; 
  c 
  is 
  unexpectedly 
  low. 
  The 
  last 
  point 
  

   requires 
  some 
  discussion. 
  According 
  to 
  a 
  mass 
  of 
  published 
  

   dew-point 
  observations, 
  a 
  value 
  0'5 
  for 
  c 
  was 
  expected 
  in 
  

   Table 
  11., 
  and 
  the 
  writer 
  thinks 
  it 
  superfluous 
  to 
  make 
  

   additional 
  dew-point 
  observations. 
  The 
  low 
  value 
  0*4 
  found 
  

   for 
  c, 
  though 
  opposed 
  somewhat 
  to 
  the 
  dew-point 
  results, 
  is 
  

   favoured 
  by 
  Maxwell's 
  theory 
  *. 
  To 
  make 
  c 
  = 
  *5 
  in 
  high 
  

  

  ventilation 
  is 
  to 
  make 
  his 
  ratio 
  ^ 
  (loc. 
  cit.) 
  practically 
  unity, 
  

  

  but 
  he 
  considers 
  it 
  probably 
  *77 
  and 
  "certainly 
  less 
  than 
  

   unity." 
  His 
  estimate 
  is 
  supported 
  by 
  the 
  experiments 
  of 
  

   Graetz, 
  Winkelmann, 
  and 
  of 
  Kundt 
  and 
  Warburg, 
  so 
  that 
  a 
  

   considerably 
  lower 
  value 
  of 
  c 
  is 
  suggested. 
  It 
  is 
  not, 
  however, 
  

   the 
  object 
  of 
  this 
  note 
  to 
  determine 
  the 
  value 
  of 
  c. 
  It 
  is 
  the 
  

   method 
  with 
  its 
  theoretical 
  and 
  practical 
  claims 
  which 
  is 
  put 
  

   forward. 
  A 
  wider 
  basis 
  was 
  rendered 
  impossible 
  from 
  want 
  

   of 
  leisure. 
  

  

  Abbasia 
  Observatory, 
  Egypt. 
  

   August 
  22, 
  1901.' 
  

  

  XLII. 
  Air-Pressures 
  used 
  in 
  playing 
  Brass 
  Instruments. 
  By 
  

   Edwin 
  H. 
  Barton, 
  JD.Sc, 
  F.R.S.E., 
  Senior 
  Lecturer 
  in 
  

   Physics 
  at 
  University 
  College, 
  Nottingham, 
  and 
  3. 
  C. 
  Laws, 
  

   B.lSc, 
  "1851 
  Exhibition" 
  Science 
  Research 
  Scholar 
  f. 
  

  

  [Plates 
  VII. 
  & 
  VIII.] 
  

  

  IT 
  is 
  well 
  known 
  that 
  in 
  playing 
  upon 
  the 
  " 
  brass 
  " 
  or 
  

   " 
  wood-wind" 
  instruments 
  of 
  the 
  orchestra 
  the 
  particular 
  

   note, 
  at 
  any 
  instant 
  desired, 
  is 
  produced 
  by 
  the 
  simultaneous 
  

   use 
  of 
  the 
  mechanism 
  of 
  the 
  instrument 
  and 
  the 
  correspond- 
  

   ing 
  " 
  embouchure/' 
  through 
  which 
  air 
  at 
  a 
  suitable 
  pressure 
  

   is 
  driven 
  by 
  the 
  performer. 
  The 
  mechanism 
  adjusts 
  the 
  

  

  * 
  Art. 
  "Diffusion," 
  Encyc. 
  Britt. 
  

  

  f 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  December 
  13, 
  1901. 
  

  

  