vironment of Ganymede as Ganymede’s environment was to
Earth’s.
A is to B as Bis towhat? To C? Or to A?
Was Rullman, in the face of the impossibility of such a
project, trying to re-adapt his people to Earth?
There should be dials or meters on this side of the wall
which would give more information as to what it was like on
the other side. And there they were, in a little hooded embra-
sure which Sweeney had overlooked in the first shock. They
said:
r 59
Degrees F.
Millibars
047 0140
Dew Point 02 Tens rnrn Hg
Some of these meant nothing to Sweeney: he had never
before encountered pressure expressed in millibars, let alone
the shorthand way it was registered on the meter before him;
nor did he know how to compute relative humidity from the
dew point. With the Fahrenheit scale he was vaguely familiar,
vaguely enough to have forgotten how to convert it into
Centigrade readings. But
Oxygen tension!
There was one planet, and one only, where such a measure-
ment could have any meaning.
Sweeney ran.
He was no longer running by the time he had reached Rull-
man’s office, although he was still thoroughly out of breath.
Knowing that he would be unable to cross back over the top
of the pantrobe lab again, feeling that heat beating up at him
and knowing at least in part what it meant, he had gone in the
opposite direction, past the gigantic heat-exchangers, and
blundered his way up from the other side. The route he had
followed had covered over three erratic miles, and several ad-
ditional discoveries which bad shaken him almost as hard as