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XXXIII.  Note  on  Archdeacon  Pratt’s  Pa;per  “ On  the  Effect  of  Local  Attraction  in  the 
English  Arc"'  By  Captain  A.  R,  Crarke,  It,E.  Communicated  hy  lAmt. -Colonel 
Jajmes,  B.E, 
Received  June  30, — Read  November  18,  1858. 
The  distances  between  the  parallels  of  latitude  of  the  principal  stations  of  the  original 
Enghsh  Arc,  as  used  by  Archdeacon  Pratt  in  his  paper  “ On  the  Effects  of  Local  Attrac- 
tion*,” are  taken  from  the  second  and  third  volumes  of  the  “Account  of  the  Trigono- 
metrical Survey.”  The  correct  distances,  with  the  exception  of  that  for  Blenheim,  are 
given  at  page  732  of  the  last  published  volume f of  the  Ordnance  Survey.  They  are  as 
follows 
Feet. 
Dunnose  and  Greenwich  .......  313716‘9 
Greenwich  and  Blenheim 132802*0 
Blenheim  and  Arbm*y  Hill 139837*4 
Arbury  HOI  and  Clifton 450225*2 
Clifton  and  Burleigh  Moor 406596*9 
The  distance,  Greenwich  to  Bleinheim,  is  not  altered,  as  there  is  no  new  determina- 
tion of  that  quantity.  The  quantities  X and  (Jt^,  as  used  by  Archdeacon  Pratt,  do  not 
require  alteration. 
The  following  Table  exhibits  the  values  of  E and  A for  the  several  arcs  .*—> 
Arc. 
Values  of  E. 
Values  of  A. 
1. 
0*18568 
*00985408 
2. 
0*15446 
*00984849 
3. 
0*13546 
‘00987075 
4. 
0*09455 
*00986928 
5. 
0*03572 
*00986262 
* Published  in  the  Philosophical  Transactions  for  1856,  Part  I.  p.  31. 
t “ Account  of  the  Observations  and  Calculations  of  the  Principal  Triangulation,  and  of  the  Figure, 
Dimensions,  and  Mean  Specific  Gravity  of  the  Earth  as  deduced  therefrom.”  Published  by  Order  of  the 
Master- General  and  Board  of  Ordnance.  London,  1858, 
5 K* 
MDCCCLVIII. 
