wing to the deliquescence of the chloride of iron with which
it was constantly combined. I think that this chloride, in accordance
with the general law, is transformed into a sulphate--a transformation
which readily occurs on Vesuvius.

15. Copious and well-crystallized sal ammoniac is only found on the
fumaroles of those lavas which have covered cultivated or wooded ground.

16. The scarcity of oxygen in the gases of fumaroles may possibly arise
from the formation of the oxides which precede the chlorides.

17. Lavas give a continuous spectrum, although covered with smoke, when
looked at with Hoffmann's spectroscope with direct vision.[G]

18. The smoke gives positive electricity, and the falling ashes negative
electricity.

REFERENCE TO THE PLATES.

PLATE

Ia. The Cone of Vesuvius, in 1870, from a Photograph taken
near the Observatory.

_a._ The Atria del Cavallo.
_b b._ Fossa della Vetrana.
_c._ Punta del Crocella.
_d._ Lava of 1858 and 1867.
_e._ Police Barrack near the Observatory.
_f._ Part of Monte Somma.

IIa. Profile of Vesuvius, taken from a Photograph of the
Observatory in the month of September, 1871.

1. The Cone, on the 13th January, 1871.
2, 2. Lava of 1871.

IIIa. Profile of Vesuvius on the 16th April, 1872, about ten
days before the last Conflagration.

IVa. Vesuvius, on the 26th April, 1872, from a Photograph taken
in the neighbourhood of Naples.

1. The Observatory.
2. Fossa della Vetrana.
3. Eruption of Smoke and Ashes, with Stones, from the
surface of the Lava.
4. The Novelle, St. Sebastiano, and Massa.
5. Lava which took the direction of Resina.
6. Lava which, from the Crater, took the direction of the
Camaldoli.
7. The Grain Stores, near Naples.
8. Resina.
9. Torre del Greco.
10. The Camaldoli.

Va. Profile of Vesuvius after the Eruption of the 26th April,
1872, from a Photograph taken near the Observatory.

1, 1. The Fissures of the 26th of April.
2, 3. Small Hill thrown up on the morning of the 26th of
April, from below which issued the great current of
Lava.
4, 4, 4. The Mouths out of which the Lava issued.
5, 5. The larger Lava Stream, which passed near the Observatory
by the Fossa della Vetrana.
6, 6. The other Lava Stream, which, after dividing from
the last, took the direction of Resina.
7, 7. Th