From:
Sir John Herschel
To:
James David Forbes
Date:
[3 March 1840]
Source of text:
St. Andrews 12 (C: RS:HS 25.6.1 & TxU:H/L-0157; Reel 1054)
Summary:
Outlines theory behind and method for preparing thermographic paper, which allows observers to determine 'what share each ray of the spectrum bears in producing the observed total effects.'
Contributor:
John Herschel Project