Search: John Herschel Project in contributor 
Herschel, John in correspondent 
Walker, James Thomas in correspondent 
1860-1869::1864::12 in date 
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From:
Sir John Herschel
To:
James Thomas Walker
Date:
[10 December 1864]
Source of text:
RS:HS 18.16 (C: 24.77)
Summary:

Received Indian survey chart. JH's son John wrote of higher-order ellipsoidal triangles with sides based on geodesical triangles. JH objects that these violate principle of diagonal bracing. Proposes different triangles and names sites in India as apexes. Received G. B. Airy's paper on reduction.

Contributor:
John Herschel Project
From:
James Thomas Walker
To:
Sir John Herschel
Date:
[9 December 1864]
Source of text:
RS:HS 18.15
Summary:

Sent JH 'Index Chart' of Great Trigonometrical Survey of India. Compares five triangulation methods: longitudinal series, George Everest's, G. B. Airy's, that of JH's son John, and minimum squares. JH's son and bride avoided cyclone that destroyed Calcutta Observatory.

Contributor:
John Herschel Project
From:
James Thomas Walker
To:
Sir John Herschel
Date:
[15 December 1864]
Source of text:
RS:HS 18.17
Summary:

Indian Triangulation chart showed progress to May 1862. Explains why arcs of meridians and parallels were chosen over diagonal braces. G. B. Airy's method of determining errors helped. Will take note and package from Maria [Herschel] to JH's son John.

Contributor:
John Herschel Project