ker steps
backwards when working his hemp. The activity now displayed on the drill-
ground is a preparation for the approaching dispersal. The travellers
are packing up.

Soon we see a few Spiders trotting briskly between the table and the open
window. They are running in mid-air. But on what? If the light fall
favourably, I manage to see, at moments, behind the tiny animal, a thread
resembling a ray of light, which appears for an instant, gleams and
disappears. Behind, therefore, there is a mooring, only just
perceptible, if you look very carefully; but, in front, towards the
window, there is nothing to be seen at all.

In vain I examine above, below, at the side; in vain I vary the direction
of the eye: I can distinguish no support for the little creature to walk
upon. One would think that the beastie were paddling in space. It
suggests the idea of a small bird, tied by the leg with a thread and
making a flying rush forwards.

But, in this case, appearances are deceptive: flight is impossible; the
Spider must necessarily have a bridge whereby to cross the intervening
space. This bridge, which I cannot see, I can at least destroy. I
cleave the air with a ruler in front of the Spider making for the window.
That is quite enough: the tiny animal at once ceases to go forward and
falls. The invisible foot-plank is broken. My son, young Paul, who is
helping me, is astounded at this wave of the magic wand, for not even he,
with his fresh, young eyes, is able to see a support ahead for the
Spiderling to move along.

In the rear, on the other hand, a thread is visible. The difference is
easily explained. Every Spider, as she goes, at the same time spins a
safety-cord which will guard the rope-walker against the risk of an
always possible fall. In the rear, therefore, the thread is of double
thickness and can be seen, whereas, in front, it is still single and
hardly perceptible to the eye.

Obviously, this invisible foot-bridge is not flung out by the animal: it
is carried and unrolled by a gust of air. The Epeira, supplied with this
line, lets it float freely; and the wind, however softly blowing, bears
it along and unwinds it. Even so is the smoke from the bowl of a pipe
whirled up in the air.

This floating thread has but to touch any object in the neighbourhood and
it will remain fixed to it. The suspension-bridge is thrown; and the
Spider can set out. The South-American Indians are said to cross th