Nevertheless, the final year of his residence in Africa saw the production of the first of the series of works on seaweeds by which his name will ever be best known. His _Manual of British Algae_ was issued by the Ray Society in 1841, its Introduction dated at Cape Town, October 1840--a modest octavo volume, characterized by the thoroughness which runs through all his work.
A period of convalescence and apathy followed his return, in which he wandered about Ireland, doing some desultory botanizing; after which he settled in his old home at Limerick, and again took up the uncongenial duties connected with the family business.
But soon a new prospect opened out. The retirement of William Allman left vacant the Chair of Botany in Dublin University. Harvey had little hesitation in applying for the post, to which, he points out to a friend, "a moderate salary and comfortable College-rooms are attached. It is an old bachelor place," he writes, "and would in many ways suit me very well. The only thing on the face of it disagreeable is the _lecturing_, but I don't think I should mind that much, as it is lawful to have the subjects for the class written down." Harvey's candidature was viewed favourably by the University authorities, but a difficulty arose, inasmuch as the School of Physic Act prescribed that the Professor of Botany should hold a medical degree, or the licence of the College of Physicians. To render him eligible, the degree of M.D. was at once conferred on Harvey _honoris causa_, but after a good deal of discussion this solution of the question was held to be inadmissible, and George James Allman was appointed to the vacant chair. Harvey, however, obtained the smaller appointment of Keeper of the University Herbarium, which had fallen vacant at about the same time owing to the death of Dr Thomas Coulter, the botanical explorer of Central Mexico and California.
Harvey now at last found himself in a congenial post, with a fair amount of leisure, and facilities for scientific work. He presented his herbarium of over 10,000 species to the University, which already possessed Coulter's extensive American collections. "I am as busy as a bee these times," he writes. "I rise at 5 a.m. or before it, and work till breakfast-time (half-past eight) at the 'Antarctic Algae[113].' Directly after breakfast I start for the College, and do not leave it till five o'clock in the evening. Again at plants till dusk. I am writing on the 'Antarctic Algae,' and arranging the Herbarium, and have been working at Coulter's Mexican and Californian plants." College vacations were now usually spent at Kew, staying with his best friend Sir William Hooker, and working hard in the Herbarium. On the way home from the first of these vacations, he went to Torquay, to spend some time with his old correspondent, Mrs Griffiths. They went out boating, he and the good lady of seventy-six years; and together they visited the only British habitat of _Gigartina Teedii_, six miles away, and gathered that coveted sea-weed in the spot where Mrs Griffiths had discovered it in 1811, the year in which Harvey was born.