﻿Electrical 
  Device 
  for 
  evaluating 
  Formulae. 
  291 
  

  

  through 
  the 
  uranyl 
  nitrate 
  itself 
  which 
  contained 
  the 
  radiating 
  

   uranium 
  X. 
  If 
  more 
  lead 
  had 
  been 
  used 
  by 
  Hackett 
  his 
  

   curves 
  would, 
  I 
  think, 
  resemble 
  those 
  in 
  fig. 
  3. 
  It 
  is 
  still 
  

   an 
  open 
  question 
  how 
  near 
  the 
  points 
  lie 
  to 
  a 
  definite 
  curve. 
  

   So 
  far 
  as 
  I 
  can 
  judge, 
  repeated 
  observations 
  and 
  increased 
  

   care 
  m 
  attention 
  to 
  details 
  tends 
  to 
  bring 
  the 
  points 
  nearer 
  

   and 
  nearer 
  the 
  curves 
  shown 
  in 
  this 
  paper, 
  which 
  for 
  soft 
  rays, 
  

   are 
  nearly 
  parabolic. 
  

  

  On 
  the 
  other 
  hand, 
  the 
  points 
  for 
  incident 
  rays 
  do 
  not 
  

   seem 
  to 
  be 
  on 
  a 
  curve 
  ; 
  and 
  there 
  is 
  therefore 
  good 
  reason 
  to 
  

   expect 
  that 
  the 
  points 
  for 
  emergent 
  rays 
  will 
  show 
  a 
  corre- 
  

   sponding 
  irregularity. 
  

  

  XXXVI. 
  The 
  Arthur 
  Wright 
  Electrical 
  Device 
  for 
  evaluating 
  

   Formulce 
  and 
  solving 
  Equations. 
  By 
  Alexander 
  Russell, 
  

   M.A., 
  D.Sc, 
  and 
  Artkue 
  Wkight, 
  M.I.E.E* 
  

  

  Table 
  of 
  Coxtents, 
  

  

  I. 
  Introduction. 
  

  

  It. 
  Historical. 
  

  

  III. 
  The 
  Slide 
  Eesistances. 
  

  

  IV. 
  Multiplication. 
  The 
  Index 
  Line. 
  

   V. 
  The 
  Contact-Fing'ers. 
  

  

  YL 
  Addition 
  and 
  Subtraction. 
  

   VII. 
  The 
  Use 
  of 
  the 
  Arms 
  of 
  the 
  Bridge. 
  

   VIII. 
  Cubic 
  Equation. 
  

   IX. 
  Equations 
  of 
  Degrees 
  higher 
  than 
  the 
  Third. 
  

   X. 
  Imaginary 
  Roots. 
  

   XI. 
  Solutions 
  of 
  Equations 
  containing 
  Miscellaneous 
  

  

  Functions. 
  

   XII. 
  Solution 
  of 
  Transcendental 
  Equations. 
  

  

  XIII. 
  Tracing 
  Curves 
  Electrically. 
  

  

  XIV. 
  Conclusion. 
  

  

  I. 
  Introduction, 
  

  

  IF 
  an 
  ordinary 
  algebraical 
  expression 
  consisting 
  of 
  several 
  

   terms 
  be 
  computed 
  by 
  the 
  slide-rule 
  or 
  by 
  logarithmic 
  

   tables, 
  each 
  term 
  must 
  be 
  computed 
  separately 
  and 
  the 
  sum 
  

   of 
  the 
  negative 
  terms 
  subtracted 
  from 
  the 
  sum 
  of 
  the 
  positive 
  

   terms. 
  If 
  all 
  these 
  operations 
  were 
  done 
  mechanically 
  

   it 
  would 
  often 
  save 
  time 
  and 
  lessen 
  the 
  risk 
  of 
  error. 
  In 
  a 
  

   few 
  cases 
  the 
  form 
  of 
  the 
  expression 
  can 
  be 
  altered 
  with 
  

   advantage 
  so 
  as 
  to 
  adapt 
  it 
  to 
  logarithmic 
  computation, 
  but 
  

   there 
  are 
  many 
  cases 
  where 
  the 
  terms 
  of 
  the 
  expression 
  have 
  

   to 
  be 
  evaluated 
  separately, 
  and 
  in 
  these 
  cases 
  it 
  saves 
  mental 
  

   labour 
  to 
  do 
  the 
  operations 
  mechanically. 
  

  

  The 
  electrical 
  device 
  described 
  below, 
  which 
  was 
  invented 
  

  

  • 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  June 
  11; 
  1909. 
  

  

  