﻿316 
  

  

  Capt. 
  W. 
  J. 
  Heaviside 
  on 
  Approximate 
  [Mar. 
  11, 
  

  

  The 
  temperature 
  in 
  the 
  shade 
  at 
  sunrise 
  was 
  53° 
  F., 
  and 
  after 
  transit 
  

   65° 
  F. 
  

  

  The 
  heliometer 
  used 
  by 
  me 
  on 
  this 
  occasion 
  was 
  constructed 
  by 
  Fraun- 
  

   hofer. 
  One 
  of 
  the 
  halves 
  of 
  the 
  object-glass 
  was 
  used, 
  the 
  line 
  of 
  separa- 
  

   tion 
  being 
  put 
  normal 
  to 
  the 
  sun's 
  limb 
  at 
  the 
  point 
  of 
  contact, 
  in 
  order 
  

   to 
  produce 
  the 
  least 
  distortion 
  of 
  image 
  in 
  the 
  direction 
  of 
  the 
  common 
  

   diameter 
  of 
  the 
  two 
  objects. 
  The 
  focal 
  length 
  of 
  the 
  instrument 
  is 
  

   nearly 
  45 
  inches 
  (English), 
  the 
  aperture 
  3 
  inches, 
  and 
  the 
  power 
  used 
  

   was 
  97. 
  

  

  Our 
  observatory 
  was 
  situated 
  about 
  half 
  a 
  mile 
  to 
  the 
  southward 
  of 
  

   Luxor, 
  in 
  lat. 
  25° 
  41' 
  40" 
  1ST., 
  as 
  determined 
  by 
  ¥m. 
  Dollen 
  and 
  Pro- 
  

   fessor 
  Auwers, 
  and 
  in 
  longitude 
  2 
  h 
  10 
  m 
  22 
  s 
  E., 
  as 
  fixed 
  by 
  Mahmoud 
  Bey 
  

   in 
  his 
  late 
  survey 
  of 
  the 
  valley 
  of 
  the 
  Nile. 
  

  

  III. 
  "Preliminary 
  Abstract 
  of 
  Approximate 
  Mean 
  Results 
  with 
  

   the 
  Invariable 
  Pendulums 
  Nos. 
  4 
  and 
  1821 
  , 
  in 
  continuation 
  

   of 
  the 
  Abstract 
  published 
  in 
  vol. 
  xix. 
  of 
  the 
  Proceedings/' 
  By 
  

   Captain 
  W. 
  J. 
  Heaviside, 
  R.E. 
  Communicated 
  by 
  Professor 
  

   Stokes, 
  Sec. 
  R.S. 
  Received 
  February 
  15, 
  1875. 
  

  

  Extract 
  from 
  a 
  Letter 
  from 
  Captain 
  Heaviside 
  to 
  Professor 
  JStoJces. 
  

  

  Dehra, 
  N. 
  W. 
  P., 
  21st 
  January, 
  1875. 
  

   My 
  deak 
  Sir, 
  — 
  An 
  abstract 
  of 
  approximate 
  results 
  by 
  the 
  invariable 
  

   pendulums 
  was 
  printed 
  under 
  Captain 
  Basevi's 
  superintendence 
  in 
  1870. 
  

   I 
  now 
  enclose 
  an 
  abstract 
  in 
  continuation, 
  bringing 
  the 
  work 
  down 
  to 
  

   Kew. 
  The 
  formulae 
  and 
  factors 
  employed 
  by 
  Basevi 
  have 
  been 
  used 
  in 
  

   the 
  reductions, 
  so 
  that 
  the 
  results 
  in 
  the 
  two 
  abstracts 
  might 
  be 
  directly 
  

   comparable. 
  

  

  The 
  observations 
  at 
  Meean 
  Meer 
  and 
  at 
  More 
  were 
  taken 
  by 
  Basevi, 
  

   and 
  the 
  reduction 
  to 
  mean 
  sea-level 
  for 
  More 
  has 
  been 
  computed 
  in 
  

   accordance 
  with 
  a 
  memorandum 
  he 
  left, 
  in 
  which 
  he 
  assumed 
  the 
  moun- 
  

   tain 
  masses 
  on 
  which 
  More 
  stands 
  to 
  compose 
  a 
  cylinder, 
  having 
  a 
  height 
  

   of 
  2-92 
  miles 
  and 
  a 
  radius 
  of 
  200 
  miles. 
  

  

  Tou 
  will 
  see 
  that 
  the 
  results 
  at 
  Kew, 
  from 
  my 
  observations 
  in 
  1873, 
  

   differ 
  by 
  0*38 
  vibration 
  from 
  those 
  obtained 
  by 
  Mr. 
  Loewy 
  in 
  1866. 
  

   My 
  observations 
  were 
  taken 
  in 
  August, 
  at 
  a 
  mean 
  temperature 
  of 
  65° 
  ; 
  

   his 
  in 
  January, 
  at 
  a 
  temperature 
  of 
  54°. 
  

  

  As 
  the 
  temperature-factor 
  (0*48 
  vibration 
  for 
  1° 
  Fahr.) 
  here 
  employed 
  

   is 
  larger 
  than 
  that 
  which 
  will 
  eventually 
  be 
  adopted, 
  the 
  difference 
  

   between 
  the 
  two 
  results 
  will 
  be 
  still 
  further 
  reduced, 
  and 
  the 
  agreement 
  

   will 
  be 
  much 
  closer 
  than 
  I 
  expected 
  to 
  obtain, 
  when 
  taking 
  into 
  con- 
  

   sideration 
  the 
  varied 
  travels 
  these 
  pendulums 
  went 
  through 
  in 
  the 
  

   interval. 
  * 
  * 
  * 
  

  

  