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 the 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 chafing-dish, on the level of the table, they float slowly upwards and, for the most part, reach the ceiling.  The emigrants’ lines should rise in the same way and even better.

The thing is done:  with the aid of nothing that is visible to the three of us looking on, a Spider makes her ascent.  She ambles with her eight legs through the air; she mounts, gently swaying.  The others, in ever-increasing numbers, follow, sometimes by different roads, sometimes by the same road.  Any one who did not possess the secret would stand amazed at this magic ascent without a ladder.  In a few minutes, most of them are up, clinging to the ceiling.