f January 8,
ozone was present in more than its usual amounts. During January 9-16, it
was absent. On January 17 it reappeared, and on January 18 it was
abundant. Similar meteorological conditions (calm and no ozone) were
found to precede previous epidemics.

Mr. Power's report, with regard to Fulham, seems conclusive, and there is
a strong impression that hospitals, other than Fulham, have served as
centers of dissemination.

In the last lecture I gave you the opinion of M. Bertillon, of Paris, and
quoted figures in support of that opinion. It is a fact of some
importance to remember that small-pox is one of those diseases which has
a peculiar odor, recognizable by the expert. As to its conveyance for
long distances through the air, there are some curious facts quoted by
Professor Waterhouse, of Cambridge, Massachusetts, in a letter addressed
to Dr. Haygarth at the close of the last century. Professor Waterhouse
states that at Boston there was a small-pox hospital on one side of a
river, and opposite it, 1,500 yards away, was a dockyard, where, on a
certain misty, foggy day, with light airs just moving in a direction from
the hospital to the dockyard, ten men were working. Twelve days later all
but two of these men were down with small-pox, and the only possible
source of infection was the hospital across the river. (_To be
continued_.)

* * * * *

SUNLIGHT COLORS.

[Footnote: Lecture delivered by Capt. W. De W. Abney, R.E., P.B.S., at
the Royal Institution, on February 25, 1887.--_Nature_.]

By Capt. W. DE W. ABNEY.

Sunlight is so intimately woven up with our physical enjoyment of life
that it is perhaps not the most uninteresting subject that can be chosen
for what is--perhaps somewhat pedantically--termed a Friday evening
"discourse." Now, no discourse ought to be be possible without a text on
which to hang one's words, and I think I found a suitable one when
walking with an artist friend from South Kensington Museum the other day.
The sun appeared like a red disk through one of those fogs which the east
wind had brought, and I happened to point it out to him. He looked, and
said, "Why is it that the sun appears so red?" Being near the railway
station, whither he was bound, I had no time to enter into the subject,
but said if he would come to the Royal Institution this evening I would
endeavor to explain the matter. I am going to redeem that promise, and to
devote at