In the harvest of 1845 a disease, hitherto unknown in Ireland, phytophthora infestans, attacked the potato crop. The disease had made its appearance some years previously in north America and shortly afterwards in Europe. There is reason to believe that it already existed in south America, and it is possible that its failure to reach Europe with the early-introduced tubers was due to diseased tubers rotting during the long voyages under ‘ sail ’. The progress of the blight in European countries in the summer and early autumn of 1845 was reported in the Dublin Evening Post, which, without raising any serious alarm, pointed out the danger to the crop in Ireland. The seriousness of a failure of the staple food of the majority of the population must have been clear to every man struck by that possibility.

Two themes are discussed in this article : first, the meaning and scope of ‘ historical geography ’ with reference to various examples; and second, the possibility that Irish historians may plan enquiries into this field as part of their research-programme. The dangers involved in any effort to unite two separate yet related fields of learning are considerable; historical geography must be based on the work of those understanding each of the specialisations involved or, at least, willing to allow their work to be tested by the knowledge of an expert in the cognate field.