the foot of the tower, he found no
ozone at the same time. He argued, therefore, that the ozone above was
used up in purifying the town below, and so suggested quite a new
explanation of the purification of air.

The subject was very soon taken up by English observers, and I
remember well a lecture upon it by Michael Faraday, in which that
illustrious philosopher, confirming Schonbein, stated that he had
discovered ozone freely on the Brighton Downs, and had found the
evidence of it diminishing as he approached Brighton, until it was
lost altogether in the town itself.

Such was the beginning of our knowledge of ozone, the precise nature
of which has not yet been completely made out. At the present time it
is held to be oxygen condensed. To use a chemical phrase, the molecule
of oxygen, which in the ordinary state is composed of two atoms, is
condensed, in ozone, as three atoms. By the electric spark discharged
in dry oxygen as much as 15 per cent. may, under proper conditions, be
turned into ozone. Ozone has also been found to be heavier than air.
Professor Zinno says, that compared with an equal volume of air its
density is equal to 1,658, and that it is forty-eight times heavier
than hydrogen. Heat decomposes it; at the temperature of boiling water
it begins to decompose. In water it is much less soluble than oxygen,
and indeed is practically insoluble; when made to bubble through
boiling water, it ceases to be ozone. The oxidizing power of ozone is
very much greater than that of oxygen, and, according to Saret, when
ozone is decomposed, one part of it enters into combination, the other
remains simply as oxygen.

It is remarkable that some substances, like turpentine and cinnamon,
absorb ozone and combine with it, a simple fact of much greater
importance than has ever been attached to it. I found, for instance,
that cinnamon which by exposure to the air has been made odorless and,
as it is said, "spoiled," can be made to reabsorb ozone and gain a
kind of freshness. It is certain also that some substances which are
supposed to have disinfecting properties owe what virtues they possess
to the presence of ozone.

On some grand scale ozone is formed in the air, and my former friend
and colleague, the late Dr. Moffatt, of Hawarden, with whom I wrote a
paper on "Meteorology and Disease," read before the Epidemiological
Society in 1852-53, described what he designated ozone periods of the
atmosphere, connecting these