Copy letter, from Sir John Herschel to Macedonio Melloni Copy of a letter. Will do all in his power to ensure that MM receives copies of the publications relating to the Fixed Observatories. Does not think MM could have seen a copy of John Frederick William Herschel's paper on photographic action when he wrote the notice in Annales de chimie. Comments on this paper and more recent experiments in this field. 23 February 1841