at open horseshoe lip, three and a half
miles straight across and over four miles following the line of the
curve, discharged a sheet of water forty feet thick at the edge into an
abyss six hundred feet below. Two islands on the brink divided this
sheet of liquid into three nearly equal parts, while myriads of
rainbows hovered in the clouds of spray. Two things especially struck
the observers: the water made but little curve or sweep on passing over
the edge, and then rushed down to the abyss at almost lightning speed,
shivering itself to infinitesimal particles on striking any rock or
projection at the side. Its behaviour was, of course, due to its
weight, and to the fact that on Jupiter bodies fall 40.98 feet the
first second, instead of sixteen feet, as on earth, and at
correspondingly increasing speed.

Finding that they were being rapidly dazed and stunned by the noise,
the travellers caused the Callisto to rise rapidly, and were soon
surveying the superb sight from a considerable elevation. Their minds
could grasp but slowly the full meaning and titanic power of what they
saw, and not even the vast falls in their nearness could make their
significance clear. Here was a sheet of water three and a half miles
wide, averaging forty feet in depth, moving at a rapid rate towards a
sheer fall of six hundred feet. They felt, as they gazed at it, that
the power of that waterfall would turn backward every engine and dynamo
on the earth, and it seemed as if it might almost put out the fires of
the sun. Yet it was but an illustration of the action of the solar orb
exerted on a vast area of ocean, the vapour in the form of rain being
afterwards turned into these comparatively narrow limits by the
topography of the continent. Compared with this, Niagara, with its
descent of less than two hundred feet, and its relatively small flow of
water, would be but a rivulet, or at best a rapid stream.
Reluctantly leaving the fascinating spectacle, they pursued their
exploration along the river above the falls. For the first few miles
the surface of the water was near that of the land; there were
occasional rapids, but few rocks, and the foaming torrent moved at
great speed, the red sandstone banks of the river being as polished as
though they had been waxed. After a while the obstructions
disappeared, but the water continued to rush and surge along at a speed
of ten or twelve miles an hour, so that it would be easily navigable