I have thought it might be of interest to the Society to lay before it a short account of some temperature observations which I succeeded in making at the Great Geysir of Iceland, in the month of August last year. As the circumstances of my visit to the island obliged me to limit my stay at that remarkable spring to a few hours, and as, during that time and for 48 hours previously, no great eruption occurred, I fear my results must appear somewhat meagre and unsatisfactory. The very interesting nature, however, of the problem of the action of the Great Geysir, and the difficulty of securing any reliable observations at all in so inaccessible a region, will perhaps be deemed sufficient grounds for my taking up the time of the Society with these few remarks. So far as my results go, they confirm very remarkably those of Professor R. Bunsen, who, with a companion, spent more than ten days at the spot in July 1846, and to whom science is indebted for the now generally received theory of the action of the Great Geysir. An account of his observations was given in the “Annalen” for 1847, and to it I shall refer frequently in the course of these remarks.