Exhibitions followed in Milan, Turin, Genoa and other cities of northern Italy, then the travelers passed into France, to the headwaters of the Rhone.

Paul had selected this river for his next voyage.

With the intention of making the entire stream from its source to the Mediterranean, he visited Geneva, in Switzerland.

Here he discovered that it would be impossible to start from the lake, as by doing so he would be carried into the great cavern known as Per du Rhone, in which the entire river disappears and makes a mysterious and unexplored passage under the mountain.

He was anxious to try the underground current through the cavern and did not give up the idea until several experiments had convinced him that it would be foolhardy to make the attempt.