This change occupied in all four seconds; and the current inwards lasted--like the outward current--twenty-two seconds, and then the whole phenomenon was repeated.

The currents kept such good time, that when I stood beyond their reach, and turned my back, I was enabled to announce each change with perfect precision.

On one occasion, the flame performed its semicircle in a horizontal instead of a vertical plane, moving round the wick in the shape of a pea-flower.

The day was very still, so that no external winds could have anything to do with this singular alternation; and, indeed, the pit was so completely sheltered by its shape, that a storm might have raged outside without producing any perceptible effect below.

It would be difficult to explain the regularity of these opposite currents, but it is not so difficult to see that some such oscillation might be expected.