Paper, 'Postscript' by John Frederick William Herschel Postscript to Herschel's paper (PT/26/11) on photographic processes. Subject: Chemistry Published in Philosophical Transactions as part of paper titled 'On the action of the rays of the solar spectrum on vegetable colours, and on some new photographic processes'. Written by Herschel in Collingwood [Kent, England]. Abstract of paper published in Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London [later Proceedings of the Royal Society of London], Volume 4, 1843. 29 August 1842