l, some days before the
last conflagration of Vesuvius, as I learnt from a letter addressed to
Signor Herzel, Swiss Consul at Palermo, communicated to me[7] by the
astronomer, Signor Cacciatore.--_Palmieri._

[G] I have made a large collection of sublimates, which I purpose
examining with the spectroscope, and I shall be able to place some at
the disposal of experimentalists who may desire to pursue investigations
of this kind.

NOTES

BY THE TRANSLATOR.

[1] (P. 82, text). Professor Palmieri has not given any description
in this Memoir of his seismograph--the instruments described being those
only which have relation to atmospheric electricity. The following brief
account of his seismograph will, therefore, form a not unsuitable
complement to his Memoir. The instrument, in general terms, is of that
class in which the wave movements are indicated by the displacement,
relative or absolute, of columns of mercury in glass tubes. It is a
self-recording instrument, composed of two distinct portions--one for
record of horizontal, or rather of what are called undulatory shocks;
the other for vertical shocks. In point of general principle, therefore,
it is very similar to that proposed by me ("Transactions, Royal Irish
Academy," in 1846), and in certain respects appears to me less
advantageous than the latter. Some account of the Palmieri instrument,
together with some critical remarks as to its action, may be found in my
"Fourth Report on Earthquakes" ("Reports, British Association, 1858,"
pp. 75-81). The following description of the instrument is derived from
"The Engineer," of 7th June, 1872, and the publishers have to thank the
proprietors of that journal for permission to use the illustration,
Plate 8.

In Fig. 1, _E_ is a helix of brass wire (gauge about one millimetre);
the helix consists of fourteen or fifteen turns, and has a diameter of
from twenty to twenty-five millimetres; it hangs from a fine metal
spring, and can be raised or lowered by a thumb screw. From the lower
end of the helix hangs a copper cone with a platinum point; the latter
is kept close to the surface of mercury in the iron basin, _f_, which
rests on an insulating column of wood or marble, _G_. The distance of
the point from the surface of the mercury remains constant, as the metal
pillar, _T_, is of such a length that its expansion or contraction by
change of temperature compensates that of the helix; the latter is in
connection (by _