e
abysses of the Cordilleras in travelling-cradles made of twisted
creepers; the little Spider passes through space on the invisible and the
imponderable.

But to carry the end of the floating thread elsewhither a draught is
needed. At this moment, the draught exists between the door of my study
and the window, both of which are open. It is so slight that I do not
feel its; I only know of it by the smoke from my pipe, curling softly in
that direction. Cold air enters from without through the door; warm air
escapes from the room through the window. This is the drought that
carries the threads with it and enables the Spiders to embark upon their
journey.

I get rid of it by closing both apertures and I break off any
communication by passing my ruler between the window and the table.
Henceforth, in the motionless atmosphere, there are no departures. The
current of air is missing, the skeins are not unwound and migration
becomes impossible.

It is soon resumed, but in a direction whereof I never dreamt. The hot
sun is beating on a certain part of the floor. At this spot, which is
warmer than the rest, a column of lighter, ascending air is generated. If
this column catch the threads, my Spiders ought to rise to the ceiling of
the room.

The curious ascent does, in fact, take place. Unfortunately, my troop,
which has been greatly reduced by the number of departures through the
window, does not lend itself to prolonged experiment. We must begin
again.

The next morning, on the same yucca, I gather the second family, as
numerous as the first. Yesterday's preparations are repeated. My legion
of Spiders first weaves a divergent framework between the top of the
brushwood placed at the emigrants' disposal and the edge of the table.
Five or six hundred wee beasties swarm all over this work-yard.

While this little world is busily fussing, making its arrangements for
departure, I make my own. Every aperture in the room is closed, so as to
obtain as calm an atmosphere as possible. A small chafing-dish is lit at
the foot of the table. My hands cannot feel the heat of it at the level
of the web whereon my Spiders are weaving. This is the very modest fire
which, with its column of rising air, shall unwind the threads and carry
them on high.

Let us first enquire the direction and strength of the current. Dandelion-
plumes, made lighter by the removal of their seeds, serve as my guides.
Released above the chafin