 In this letter Mr. Mullaney suggested that William Herschel's original catalogue of 2,500 objects would be an excellent basis for deep sky object selection for amateur astronomers looking for a challenge after completing the Messier Catalogue.The Herschel 400 is a subset of John Herschel's "General Catalogue of Nebulae and Clusters" published in 1864 of 5,000 objects, and hence also of the "New General Catalogue".The catalogue forms the basis of the Astronomical League's Herschel 400 club.