h tint as themselves.

As the action of the light continued, the first cloud gradually
resolved itself into a series of parallel disks of exquisite delicacy,
which rotated round an axis perpendicular to their surfaces, and
finally blended to a screw surface with an inclined generatrix. This
gradually changed into a filmy funnel, from the narrow end of which
the 'cord' extended to the cloud in advance.

The latter also underwent slow but incessant modification. It first
resolved itself into a series of strata resembling those of the
electric discharge. After a little time, and through changes which it
was difficult to follow, both clouds presented the appearance of a
series of concentric funnels set one within the other, the interior
ones being seen through the outer ones. Those of the distant cloud
resembled claret-glasses in shape. As many as six funnels were thus
concentrically set together, the two series being united by the
delicate cord of cloud already referred to. Other cords and Blender
tubes were afterwards formed, which coiled themselves in delicate
spirals around the funnels.

Rendering the light along the connecting-cord more intense, it
diminished in thickness and became whiter; this was a consequence of
the enlargement of its particles. The cord finally disappeared, while
the funnels melted into two ghost-like films, shaped like parasols.
They were barely visible, being of an exceedingly delicate blue tint.
They seemed woven of blue air. To compare them with cobweb or with
gauze would be to liken them to something infinitely grosser than
themselves.

In all cases a distant candle-flame, when looked at through the cloud,
was sensibly undimmed.

2. ON THE BLUE COLOUR OF THE SKY, AND THE POLARISATION OF SKYLIGHT.

[Footnote: In my 'Lectures on Light' (Longman), the polarisation of
light will be found briefly, but, I trust, clearly explained.]

1869.

After the communication to the Royal Society of the foregoing brief
account of a new Series of Chemical Reactions produced by Light, the
experiments upon this subject were continued, the number of substances
thus acted on being considerably increased.

I now, however, beg to direct attention to two questions glanced at
incidentally in the preceding pages--the blue colour of the sky, and
the polarisation of skylight. Reserving the historic treatment of the
subject for a more fitting occasion, I would merely mention now that
these questions co