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1840-1849::1849::03::08 in date 
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From:
John Johnstone
To:
Sir John Herschel
Date:
[8 March 1849]
Source of text:
TxU:H/M-0304; Reel 1087
Summary:

Sends sample of photographic lenses ground by JJ. Asks JH for formula of curvature to admit more light.

Contributor:
John Herschel Project
From:
Sir John Herschel
To:
George Biddell Airy
Date:
[8 March 1849]
Source of text:
RGO 6.160.78
Summary:

Tells GA about the internal counterpoise system in use in some German telescope mountings, and includes a diagram; JH knows nothing about chilling speculum metal [see GA's 1849-3-7].

Contributor:
John Herschel Project