We then measured the outside of the rock, and ascertained that the floor of the grotto was near the same level as the ground outside.

We remembered your lessons, father, and made some experiments to discover if it contained mephitic air.

We first lighted some candles, which were not extinguished; we then kindled a large heap of sticks and dried grass, which-burned well, the smoke passing through the opening like a chimney.

Having no uneasiness about this, we deferred our commencement till the next day.

Then we lighted the forge, and pointed some iron bars we found in the magazine; these were to be our tools to break open the rock.