﻿1875.] 
  Continuous 
  Self-registering 
  Thermometer. 
  

  

  385 
  

  

  him, 
  acting 
  upon 
  mercury 
  in 
  an 
  open 
  tube, 
  his 
  instrument 
  must 
  be 
  

   regarded 
  more 
  as 
  a 
  barometer 
  than 
  as 
  a 
  means 
  of 
  measuring 
  the 
  tem- 
  

   perature 
  of 
  the 
  atmosphere. 
  

  

  My 
  instrument 
  is 
  divided 
  into 
  two 
  portions 
  : 
  — 
  1st, 
  the 
  thermometer, 
  

   which 
  marks 
  the 
  degrees 
  ; 
  2ndly, 
  the 
  clockwork, 
  which 
  indicates 
  the 
  

   hours 
  and 
  minutes. 
  

  

  The 
  thermometer 
  shall 
  be 
  first 
  described. 
  The 
  form 
  in 
  which 
  it 
  was 
  

   originally 
  made, 
  and 
  which 
  perhaps 
  serves 
  best 
  for 
  illustrating 
  the 
  

   principle, 
  was 
  the 
  following 
  : 
  — 
  

  

  A 
  glass 
  bulb, 
  rather 
  more 
  than 
  an 
  inch 
  in 
  diameter, 
  ends 
  in 
  a 
  glass 
  

   tube 
  12 
  inches 
  long, 
  having 
  a 
  bore 
  of 
  J 
  inch. 
  This 
  tube 
  is 
  coiled 
  round 
  

   the 
  bulb 
  in 
  such 
  a 
  manner 
  as 
  to 
  form 
  a 
  complete 
  circle 
  4 
  inches 
  in 
  

   diameter, 
  the 
  bulb 
  being 
  in 
  the 
  centre 
  of 
  this 
  circle. 
  

  

  Fixed 
  to 
  opposite 
  poles 
  of 
  the 
  bulb, 
  exactly 
  at 
  right 
  angles 
  to 
  the 
  

   encircling 
  tube, 
  are 
  two 
  needle-pointed 
  pivots. 
  These 
  pivots 
  work 
  in 
  

   minute 
  metal 
  depressions 
  fixed 
  to 
  the 
  sides 
  of 
  two 
  parallel 
  uprights. 
  

  

  It 
  will 
  be 
  seen 
  from 
  this 
  arrangement 
  that 
  the 
  bulb 
  with 
  its 
  glass 
  tube 
  

   will 
  rotate 
  freely 
  between 
  the 
  uprights, 
  and 
  the 
  pivots 
  will 
  be 
  the 
  centre 
  

   of 
  a 
  circle, 
  the 
  circumference 
  of 
  which 
  is 
  formed 
  by 
  the 
  glass 
  tube. 
  

  

  The 
  bulb 
  is 
  filled 
  with 
  spirit 
  in 
  such 
  quantity 
  that 
  at 
  60° 
  Fahrenheit 
  

   the 
  spirit 
  will 
  fill 
  not 
  only 
  the 
  bulb, 
  but 
  about 
  4 
  inches 
  of 
  the 
  tube. 
  

   Mercury 
  is 
  then 
  passed 
  into 
  the 
  tube 
  till 
  it 
  comes 
  into 
  contact 
  with 
  the 
  

   spirit, 
  and 
  in 
  such 
  quantity 
  as 
  to 
  fill 
  up 
  about 
  3 
  inches 
  of 
  the 
  remaining 
  

   portion 
  of 
  the 
  tube. 
  

  

  The 
  spirit 
  is 
  now 
  heated 
  to 
  120°, 
  and 
  as 
  it 
  expands 
  forces 
  the 
  column 
  

   of 
  mercury 
  in 
  front 
  of 
  it 
  till 
  the 
  mercury 
  comes 
  within 
  | 
  inch 
  of 
  the 
  end 
  

   of 
  the 
  tube. 
  The 
  tube 
  is 
  then 
  hermetically 
  sealed, 
  enclosing 
  a 
  small 
  

   quantity 
  of 
  air. 
  

  

  If 
  the 
  thermometer 
  be 
  now 
  arranged 
  with 
  its 
  needle-points 
  between 
  

   the 
  uprights, 
  it 
  will 
  be 
  observed 
  that, 
  as 
  the 
  spirit 
  contracts 
  on 
  cooling, 
  it 
  

   draws 
  the 
  column 
  of 
  mercury 
  with 
  it. 
  This 
  immediately 
  alters 
  the 
  

   centre 
  of 
  gravity, 
  and 
  the 
  bulb 
  and 
  tube 
  begin 
  to 
  revolve 
  in 
  a 
  direction 
  

   opposite 
  to 
  that 
  of 
  the 
  receding 
  mercury. 
  

  

  On 
  again 
  applying 
  heat, 
  and 
  the 
  mercury 
  passing 
  forwards, 
  the 
  bulb 
  

   regains 
  its 
  original 
  position. 
  

  

  By 
  this 
  simple 
  arrangement, 
  the 
  two 
  forces, 
  heat 
  and 
  gravity, 
  acting 
  

   in 
  contrary 
  directions, 
  generate 
  a 
  beautifully 
  steady 
  rotatory 
  movement. 
  

  

  The 
  method 
  by 
  which 
  this 
  movement 
  is 
  made 
  serviceable 
  for 
  moving 
  

   the 
  register 
  will 
  now 
  be 
  described. 
  

  

  A 
  grooved 
  wheel, 
  2 
  inches 
  in 
  diameter, 
  is 
  fixed 
  to 
  one 
  of 
  the 
  central 
  

   pivots, 
  therefore 
  revolving 
  with 
  the 
  bulb. 
  Directly 
  above 
  and 
  at 
  a 
  

   distance 
  of 
  7 
  inches 
  from 
  this 
  wheel 
  is 
  fixed 
  between 
  needle-points 
  

   another 
  wheel 
  of 
  exactly 
  similar 
  size. 
  Around 
  and 
  between 
  these 
  two 
  

   wheels 
  passes 
  a 
  minute 
  endless 
  chain. 
  

  

  