the external
atmosphere was very thin indeed. This I had anticipated. Gravity on
the surface of Mars is less than half what it is on Earth; the total
mass of the planet is as two to fifteen. It was consequently to be
expected that the extent of the Martial atmosphere, and its density
even at the sea-level, would be far less than on the heavier planet.
Rigging the air-pump securely round the aperture, exhausting its
chamber, and permitting the Martial air to fill it, I was glad to find
a pressure equal to that which prevails at a height of 16,000 feet on
Earth. Chemical tests showed the presence of oxygen in somewhat
greater proportion than in the purest air of terrestrial mountains. It
would sustain life, therefore, and without serious injury, if the
change from a dense to a light atmosphere were not too suddenly made.
I determined then gradually to diminish the density of the internal
atmosphere to something not very much greater than that outside. For
this purpose I unrigged the air-pump apparatus, and almost, but not
quite, closed the valve, leaving an aperture about the twentieth part
of an inch in diameter. The silence was instantly broken by a whistle
the shrillest and loudest I had ever heard; the dense compressed
atmosphere of the Astronaut rushing out with a force which actually
created a draught through the whole vessel, to the great discomfiture
of the birds, which roughed their feathers and fluttered about in
dismay. The pressure gauge fell with astonishing rapidity, despite the
minuteness of the aperture; and in a few minutes indicated about 24
barometrical inches. I then checked the exit of the air for a time,
while I proceeded to loosen the cement around the window by which I
had entered, and prepared for my exit. Over a very light flannel
under-vesture I put on a mail-shirt of fine close-woven wire, which
had turned the edge of Mahratta tulwars, repelled the thrust of a
Calabrian stiletto, and showed no mark of three carbine bullets fired
point-blank. Over this I wore a suit of grey broadcloth, and a pair of
strong boots over woollen socks, prepared for cold and damp as well as
for the heat of a sun shining perpendicularly through an Alpine
atmosphere. I had nearly equalised the atmospheric pressure within and
without, at about 17 inches, before the first beams of dawn shone
upward on the ceiling of the Astronaut. A few minutes later I stepped
forth on the platform, some two hundred yards in circumferenc