Drawing of apparatus of J. H. J. Müller to simulate a geyser. If the tube "ab" be ﬁlled with water and heated at two points, ﬁrst at "a" and then at "b", the following succession of changes is produced. The water at "a" beginning to boil, the superincumbent column is consequently raised, and the stratum of water which was on the point of boiling at "b" being raised to "d" is there subjected to a diminished pressure; a sudden evolution of steam accordingly takes place at "d", and the superincumbent water is violently ejected. Received in the basin "c", the air—cooled water sinks back into the tube, and the temperature of the whole column is consequently lowered; but the under strata of water are naturally those which are least affected by the cooling process; the boiling begins again at "a", and the same succession of events is the result.