﻿ARTICLE 
  XIII. 
  

  

  Practical 
  Rule 
  for 
  Calculating, 
  from 
  the 
  Elements 
  in 
  the 
  Nautical 
  

   Almanac, 
  the 
  Circumstances 
  of 
  an 
  Eclipse 
  of 
  the 
  Sun, 
  for 
  a 
  Particular 
  

   Place. 
  By 
  John 
  Gummere, 
  Teacher 
  of 
  Natural 
  Philosophy 
  and 
  Ma- 
  

   thematics 
  in 
  the 
  Friends' 
  School 
  at 
  Haverford, 
  Pennsylvania. 
  Bead 
  

   March 
  Qth, 
  1835. 
  

  

  The 
  following 
  rule, 
  deduced 
  from 
  a 
  known 
  formula, 
  gives, 
  with 
  

   little 
  labour, 
  the 
  different 
  circumstances 
  of 
  an 
  eclipse 
  of 
  the 
  sun, 
  very 
  

   nearly 
  ; 
  the 
  greatest 
  error 
  in 
  time 
  seldom 
  exceeding 
  half 
  a 
  minute. 
  

   It 
  also 
  furnishes 
  certain 
  data 
  that 
  facilitate 
  the 
  exact 
  calculation, 
  when 
  

   this 
  is 
  required. 
  The 
  multiplication 
  of 
  quantities 
  by 
  the 
  sine, 
  or 
  co- 
  

   sine 
  of 
  an 
  arc 
  or 
  angle, 
  is 
  performed 
  by 
  a 
  Traverse 
  Table, 
  as 
  in 
  Hen- 
  

   derson's 
  method 
  of 
  Predicting 
  Occultations, 
  given 
  in 
  the 
  fourth 
  vo- 
  

   lume 
  of 
  the 
  Memoirs 
  of 
  the 
  Astronomical 
  Society 
  of 
  London. 
  The 
  

   rule 
  is 
  adapted 
  to 
  the 
  use 
  of 
  the 
  traverse 
  tables 
  usually 
  contained 
  in 
  

   treatises 
  on 
  Surveying. 
  In 
  these 
  tables, 
  the 
  difference 
  of 
  latitude 
  and 
  

   the 
  departure 
  are 
  given 
  for 
  every 
  quarter 
  of 
  a 
  degree, 
  of 
  course, 
  from 
  

   0° 
  to 
  90° 
  ; 
  and 
  but 
  little 
  error 
  results, 
  if 
  the 
  required 
  quantity 
  is 
  

   taken 
  in 
  the 
  column 
  corresponding 
  to 
  the 
  course 
  which 
  is 
  nearest 
  to 
  

   the 
  given 
  angle, 
  without 
  correction 
  for 
  the 
  difference 
  between 
  the 
  

   two. 
  It 
  is, 
  however, 
  easy 
  to 
  estimate 
  and 
  apply 
  the 
  proportional 
  part, 
  

   corresponding 
  to 
  this 
  difference 
  ; 
  and 
  it 
  is 
  better 
  to 
  do 
  so. 
  When 
  the 
  

   VOL,, 
  v.— 
  3 
  z 
  

  

  