`Hello, my boys,' I said, when I discovered what they were about, `that is not the way to set to work. Geometry will simplify the operation considerably; with its help the altitude of the highest mountains are ascertained; we may, therefore, easily find the height of that branch.'
So saying, I measured out a certain distance from the base of the tree and marked the spot, and then by means of a rod, whose length I knew, and imaginary lines, I calculated the angle subtended by the trunk of the tree from the ground to the root of the branch. This done, I was able to discover the height required, and, to the astonishment of the younger children, announced that we should henceforth live thirty feet above the ground. This I wanted to know, that I might construct a ladder of the necessary length
