it, as the comet was receding towards the cold and dark depths of
space. The head was only a few miles in diameter, for it was a
small comet, and was composed of grains and masses of stone and
meteoric iron. Many of the grains were no larger than peas or
mustard-seeds; no mass was more than four feet in diameter, and
all of them had very irregular shapes. The space between the
particles was never less than one hundred times their masses.

"We can move about within it," said Ayrault, as the Callisto
entered the aggregation of particles, and moved slowly forward
among them.

The windows in the dome, being made of toughened glass, set
somewhat slantingly so as to deflect anything touching them, and
having, moreover, the pressure of the inside air to sustain them,
were fairly safe, while the windows in the sides and base were
but little exposed. Whenever a large mass seemed dangerously
near the glass, they applied an apergetic shock to it and sent it
kiting among its fellows. At these times the Callisto recoiled
slightly also, the resulting motion in either being in inverse
ratio to its weight. There was constant and incessant movement
among the individual fragments, but it was not rotary. Nothing
seemed to be revolving about anything else; all were moving,
apparently swinging back and forth, but no collisions took place.
When the separate particles got more than a certain distance
apart they reapproached one another, but when seemingly within
about one hundred diameters of each other they swung off in some
other direction. The motion was like that of innumerable
harp-strings, which may approach but never strike one another.
After a time the Callisto seemed to become endowed with the same