I must mention now that the pasture-lands of my native village lay alongside of territory of a score of square miles which in some years were all planted in corn. During the months of August and September these vast corn-fields were like deep forests. Not far from Idvor and to the east of the corn-fields was a Rumanian settlement which was notorious for its cattle-thieves. The trick of these thieves was to hide in the corn-fields at night and to wait until some cattle strayed into these fields, when they would drive them away and hide them somewhere in their own corn-fields on the other side of their own village. To prevent the herd from straying into the corn-fields at night was a great task, for the performance of which the boys had to be trained in daytime by their experienced leader. It goes without saying that each day we boys first worked off our superfluous energy in wrestling, swimming, hockey, and other strenuous games, and then settled down to the training in the arts of a herdsman which we had to practise at night. One of these arts was signalling through the ground. Each boy had a knife with a long wooden handle. This knife was stuck deep into the ground. A sound was made by striking against the wooden handle, and the boys, lying down and pressing their ears close to the ground, had to estimate the direction and the distance of the origin of sound. Practice made us quite expert in this form of signalling. We knew at that time that the sound travelled through the ground far better than through the air, and that a hard and solid ground transmitted sound much better than the ploughed-up ground. We knew, therefore, that the sound produced this way near the edge of the pasture-land could not be heard in the soft ground of the corn-fields stretching along the edge. A Rumanian cattle-thief, hidden at night in the corn-fields, could not hear our ground signals and could not locate us. Kos, the Slovenian, my teacher and interpreter of physical phenomena, could not explain this, and I doubt very much whether the average physicist of Europe at that time could have explained it. It is the basis of a discovery which I made about twenty-five years after my novel experiences in that herdsmen’s summer school in Idvor. * * * * *