abroad will know what
the effect is. A painting in the Alps, at any high elevation, is rarely
pleasing, although it may be true to nature. It looks cold, and somewhat
harsh and blue.

In London we are often favored with easterly winds, and these, unpleasant
in other ways, are also destructive of that portion of the sunlight which
is the most chemically active on living organisms. The sunlight
composition of a July day may, by the prevalence of an easterly wind, be
reduced to that of a November day, as I have proved by actual
measurement. In this case it is not the water particles which act as
scatterers, but the carbon particles from the smoke.

Knowing, then, the cause of the change in the color of sunlight, we can
make an artificial sunset, in which we have an imitation light passing
through increasing thicknesses of air largely charged with water
particles. [The image of a circular diaphragm placed in front of the
electric light was thrown on the screen in imitation of the sun, and a
cell containing hyposulphite of soda placed in the beam. Hydrochloric
acid was then added; as the fine particles of sulphur were formed, the
disk of light assumed a yellow tint, and as the decomposition of the
hyposulphite progressed, it assumed an orange and finally a deep red
tint.] With this experiment I terminate my lecture, hoping that in some
degree I have answered the question I propounded at the outset--why the
sun is red when seen through a fog.

* * * * *

THE WAVE THEORY OF SOUND CONSIDERED.

By HENRY. A. MOTT, Ph.D., LL.D.

Before presenting any of the numerous difficulties in the way of
accepting the wave theory of sound as correct, it will be best to briefly
represent its teachings, so that the reader will see that the writer is
perfectly familiar with the same.

The wave theory of sound starts off with the assumption that the
atmosphere is _composed of molecules_, and that these supposed molecules
are free to vibrate when acted upon by a vibrating body. When a tuning
fork, for example, is caused to vibrate, it is _assumed_ that the
supposed molecules in front of the advancing fork are crowded closely
together, thus forming a condensation, and on the retreat of the fork are
separated more widely apart, thus forming a rarefaction. On account of
the crowding of the molecules together to form the condensation, the air
is supposed to become more dense and of a higher temperature,