﻿386 
  On 
  a 
  Continuous 
  Self-registering 
  Thermometer. 
  [Apr. 
  29, 
  

  

  To 
  the 
  chain 
  is 
  fixed 
  a 
  tiny 
  pencil, 
  which 
  will 
  be 
  carried 
  backwards 
  

   and 
  forwards 
  between 
  the 
  wheels 
  in 
  a 
  perpendicular 
  line. 
  

  

  This 
  constitutes 
  the 
  register 
  worked 
  by 
  the 
  thermometer. 
  

  

  The 
  clockwork 
  portion 
  of 
  the 
  machine 
  is 
  so 
  arranged 
  that 
  it 
  causes 
  a 
  

   vertical 
  cylinder, 
  4 
  inches 
  diameter 
  and 
  5 
  inches 
  in 
  length, 
  to 
  revolve 
  

   once 
  in 
  24 
  hours. 
  B-ound 
  this 
  cylinder 
  is 
  fixed 
  a 
  piece 
  of 
  paper 
  12 
  inches 
  

   long, 
  5 
  inches 
  wide. 
  On 
  the 
  paper 
  in 
  the 
  direction 
  of 
  its 
  greatest 
  length 
  

   are 
  ruled 
  100 
  lines, 
  inch 
  apart, 
  each 
  indicating 
  1° 
  Fahrenheit. 
  Across 
  

   the 
  paper, 
  at 
  right 
  angles 
  to 
  these 
  lines, 
  are 
  ruled 
  twenty-four 
  lines 
  in 
  

   dark 
  ink, 
  indicating 
  the 
  hours 
  ; 
  between 
  these 
  three 
  others, 
  more 
  lightly 
  

   marked, 
  for 
  the 
  quarters. 
  The 
  cylinder 
  is 
  so 
  placed 
  that, 
  as 
  it 
  revolves, 
  

   the 
  surface 
  of 
  the 
  paper 
  is 
  y 
  1 
  ^ 
  of 
  an 
  inch 
  away 
  from 
  the 
  point 
  of 
  the 
  

   pencil 
  register 
  moving 
  at 
  right 
  angles 
  to 
  its 
  surface. 
  

  

  A 
  small 
  striker 
  is 
  connected 
  with 
  the 
  clockwork 
  in 
  such 
  a 
  manner 
  that 
  

   every 
  5 
  minutes 
  (or 
  oftener 
  if 
  required) 
  it 
  gives 
  the 
  pencil 
  a 
  gentle 
  tap, 
  

   thus 
  striking 
  its 
  point 
  against 
  the 
  paper. 
  

  

  By 
  this 
  means 
  all 
  friction 
  of 
  the 
  moving 
  pencil 
  against 
  the 
  paper 
  is 
  

   avoided, 
  and 
  the 
  index 
  is 
  marked 
  by 
  a 
  series 
  of 
  dots. 
  

  

  In 
  the 
  model 
  which 
  I 
  bring 
  before 
  the 
  Society, 
  the 
  arrangement 
  of 
  the 
  

   bulb 
  is 
  somewhat 
  modified, 
  for 
  a 
  spiral 
  coil 
  of 
  glass 
  tube 
  is 
  made 
  to 
  take 
  

   its 
  place. 
  By 
  this 
  means 
  not 
  only 
  is 
  a 
  larger 
  surface 
  of 
  the 
  spirit 
  

   exposed 
  to 
  the 
  air, 
  making 
  the 
  thermometer 
  more 
  delicate, 
  but 
  also 
  all 
  

   fear 
  of 
  the 
  mercury 
  being 
  drawn 
  into 
  the 
  bulb 
  is 
  obviated. 
  

  

  The 
  last 
  turn 
  of 
  the 
  spiral 
  coil 
  is 
  made 
  as 
  a 
  perfectly 
  true 
  circle 
  with 
  a 
  

   diameter 
  of 
  4 
  inches. 
  

  

  The 
  spiral 
  within 
  this 
  circle 
  is 
  made 
  of 
  such 
  a 
  size 
  that 
  each 
  degree 
  of 
  

   heat 
  applied 
  to 
  the 
  contained 
  spirit 
  shall 
  force 
  the 
  mercury 
  y 
  1 
  ^ 
  of 
  an 
  inch 
  

   along 
  the 
  circle. 
  

  

  Since 
  the 
  wheel 
  moving 
  the 
  register 
  equals 
  2 
  inches 
  diameter, 
  or 
  only 
  

   half 
  the 
  diameter 
  of 
  the 
  mercurial 
  circle, 
  the 
  pencil 
  will 
  move 
  of 
  an 
  

   inch 
  for 
  each 
  degree 
  of 
  heat. 
  

  

  In 
  some 
  of 
  the 
  earlier 
  experiments 
  performed, 
  I 
  found 
  that 
  in 
  straight 
  

   tubes 
  the 
  spirit 
  had 
  a 
  tendency 
  to 
  pass 
  the 
  mercurial 
  column 
  without 
  

   moving 
  it. 
  This, 
  however, 
  is 
  not 
  the 
  case 
  when 
  the 
  tube 
  forms 
  a 
  portion 
  

   of 
  a 
  circle, 
  for 
  the 
  pressure 
  of 
  the 
  mercury 
  at 
  the 
  lowest 
  portion 
  of 
  the 
  

   segment 
  prevents 
  the 
  spirit 
  passing 
  the 
  mercury. 
  

  

  I 
  trust 
  that 
  I 
  have 
  made 
  this 
  description 
  of 
  the 
  thermometer 
  intelli- 
  

   gible 
  ; 
  but 
  a 
  glance 
  at 
  the 
  working 
  model 
  which 
  I 
  have 
  the 
  honour 
  of 
  

   bringing 
  before 
  the 
  Society 
  will 
  at 
  once 
  explain 
  the 
  details 
  of 
  the 
  

   machine. 
  

  

  The 
  Society 
  then 
  adjourned 
  over 
  Ascension 
  Day, 
  to 
  Thursday, 
  

   May 
  13th. 
  

  

  