The three months' stay at Geneva at an end, the small party, bidding farewell to their hospitable and kindly host, De la Rive, turned south again. In De la Rive, Michael, by his intelligence, his scientific enthusiasm, and his unassuming cheerful disposition had won a life-long friend. The route south may well be described briefly in Michael's own words, from a letter to his mother written early in November at Rome: "On leaving Geneva we entered Switzerland, and traversed that mountainous and extraordinary country with health and fine weather, and were much diverted with the curious dresses and customs of the country.... From Switzerland we passed through the States of Baden, on the Lake of Constance (they are very small), across an arm of the kingdom of Wurtemburg, and into Bavaria. In this route we had seen, though slightly, Lausanne, Vevey, Zurich, Schaffhausen and the falls of the Rhine, in Switzerland, and Munich, and many other towns in Germany. On leaving Munich we proceeded to and across the Tyrol, and got to Padua, and from Padua to Venice. You will remember very well, I have no doubt, the picture which hung in the parlour over the fireplace, and which represented the Rialto and the Great Canal of this town. The first I have had the pleasure of crossing several times, and the second I have partly traversed in a Venetian gondola.... After seeing Venice for three days we left it, and came towards Italy, passing Bologna and Florence." Before reaching Florence the two philosophers went out of their way to inquire into a phenomenon at Pietra Mala which was much talked about. From certain tracts of ground in the neighbourhood sheets of flame of various sizes were said to burst out; the fire was said to burn anything combustible, although the ground where the flames were was not even heated; locally, it was said to be the remains of an ancient volcano. "Though it was raining hard, yet that would not deter Sir Humphry from visiting those places; but, at the same time, it made us wish to be as quick as possible. Sir Humphry therefore went to the first place, and I went to the _Acqua bollenti_, conducted by a man of the village, who carried some fire, some straw, and some water. I found the place in a cultivated field, not far from a mountain, apparently of limestone. It was simply a puddle perhaps formed by the present showers of rain. Much gas rose from the earth, and passed through the water, which made it appear boiling, and had given rise to its name; but the water and the ground were quite cold. I made another puddle with the water we brought, near the one I found there, and I saw that the gas rose up through it also; and it appeared to be continually passing off from a surface of more than eighteen inches in diameter. The soil appeared deep, and close to the spot supported vegetation readily. The man inflamed some straw, and then laid it on the ground; immediately the gas inflamed, and the flame spread to some distance from the straw