move with spades; and we began to hope. After a few days’ more labour, we found we had advanced about seven feet. Fritz wheeled out the rubbish, and formed a sort of terrace with it before the opening; while I was working at the higher part, Jack, as the least, worked below. One morning he was hammering an iron bar, which he had pointed at the end, into the rock, to loosen the earth, when he suddenly cried out—
"Papa! papa! I have pierced through!"
"Not through your hand, child?" asked I.
"No, papa!" cried he; "I have pierced through the mountain! Huzza!"
Fritz ran in at the shout, and told him he had better have said at once that he had pierced through the earth! But Jack persisted that, however his brother might laugh, he was quite sure he had felt his iron bar enter an empty space behind. I now came down from my ladder, and, moving the bar, I felt there was really a hollow into which the rubbish fell, but apparently very little below the level we were working on. I took a long pole and probed the cavity, and found that it must be of considerable size. My boys wished to have the opening enlarged and to enter immediately, but this I strictly forbade; for, as I leaned forward to examine it through the opening, a rush of mephitic air gave me a sort of vertigo. "Come away, children," cried I, in terror; "the air you would breathe there is certain death." I explained to them_ that, under certain circumstances, carbonic acid gas was frequently accumulated in caves or grottoes, rendering the air unfit for respiration; producing giddiness of the head, fainting, and eventually death. I sent them to collect
