Here an important change of life awaited him. G. J. Allman succeeded to the Natural History chair in Edinburgh, rendered vacant by the death of Edward Forbes, and Harvey was elected to the chair in Trinity College, Dublin, the difficulties which led to his rejection twelve years earlier being not raised on this occasion, though the law remained the same. At the same time, the incorporation of the several Dublin Society professorships in the newly founded Museum of Irish Industry (now the Royal College of Science for Ireland), gave him additional work, as his post was converted into a Natural History and Economic chair. However, the considerable increase of lecturing and teaching thus brought upon him did not prevent his pushing on vigorously with the now large arrears of phycological work. His first action was to finish and publish the third and last section of the _Nereis Boreali-Americana_ and then bring to a conclusion his enumeration of the seaweed flora of North America. This was accomplished in 1858, and in the same year he began the publication of the results of his work in Australia. The _Phycologia Australica_, which was issued in parts during the ensuing five years, ran to five volumes, each containing sixty coloured plates, and descriptions of all the species known from Australasian waters. In the year following the launching of this work, he commenced the publication of two important treatises on the phanerogamic flora of South Africa. In the first of these, the well-known _Flora Capensis_, he had the co-operation of Dr O. W. Sonder of Hamburg. This extensive work he did not live to complete; the third volume, which ran as far as the end of the Campanulaceae, being published the year before his death. The other work was his _Thesaurus Capensis_, a series of plates of rare or interesting South African plants, designed to supplement and illustrate the unillustrated _Flora_; of this he lived to issue only two volumes, each containing one hundred plates.