﻿310 
  PRACTICAL, 
  RULE 
  FOR 
  CALCULATING 
  

  

  mean 
  time. 
  The 
  true 
  times 
  of 
  beginning 
  and 
  end, 
  expressed 
  in 
  Phi- 
  

   ladelphia 
  mean 
  time, 
  will 
  be 
  

  

  h. 
  m. 
  sec. 
  

  

  Beginning. 
  59 
  48 
  

  

  End, 
  3 
  37 
  48 
  

  

  It 
  thus 
  appears 
  that 
  in 
  the 
  present 
  example 
  the 
  time 
  of 
  beginning, 
  

   as 
  found 
  in 
  the 
  foregoing 
  rule, 
  differs 
  only 
  12 
  seconds 
  from 
  the 
  true 
  

   time, 
  and 
  that 
  the 
  time 
  of 
  end 
  exactly 
  corresponds 
  with 
  that 
  obtained 
  

   by 
  the 
  exact 
  calculation. 
  

  

  In 
  these 
  calculations 
  no 
  allowance 
  has 
  been 
  made 
  for 
  irradiation 
  and 
  

   inflexion. 
  To 
  make 
  this 
  allowance 
  we 
  must 
  diminish 
  k, 
  by 
  subtract- 
  

   ing 
  from 
  it 
  the 
  quotient 
  of 
  ten 
  times 
  the 
  assumed 
  value 
  of 
  these 
  quan- 
  

   tities, 
  divided 
  by 
  the 
  difference 
  of 
  the 
  parallaxes 
  in 
  seconds. 
  If 
  we 
  

   assume 
  an 
  irradiation 
  and 
  inflexion, 
  amounting 
  to 
  5", 
  its 
  effect 
  in 
  the 
  

   present 
  eclipse 
  will 
  be 
  to 
  make 
  the 
  time 
  of 
  beginning, 
  at 
  Philadelphia. 
  

   13 
  seconds 
  later, 
  and 
  the 
  time 
  of 
  end 
  11 
  seconds 
  earlier 
  than 
  as 
  above 
  

   obtained. 
  Thus 
  we 
  should 
  have 
  

  

  h. 
  m. 
  sec. 
  

   Beginning 
  at 
  10 
  1 
  

  

  End 
  at 
  3 
  37 
  37. 
  

  

  