When it had been decided to come to the moon in quest for the field of
diamonds, certain changes had been made in the _Annihilator_ to fit it
for new conditions that might be met. One of these consisted of an
aperture in the two sides of the projectile permitting certain delicate
instruments to be thrust out, so that the conditions they indicated
could be read on dials or graduated scales from within.

"We will first make a test of the temperature," said Mr. Roumann, "as
that will be the easiest." Accordingly a thermometer was put outside,
and those in the air-craft anxiously watched the red column of spirits.
The temperature was marked as seventy-five inside the _Annihilator_,
but the thermometer had not been outside more than a second before
it began falling.

"Good!" exclaimed Mr. Henderson, as he noted it. "The temperature is
going down. I'd rather have it too cold than too hot. We can stand a
minus fifty of cold better than two hundred and twelve of heat. We have
fur garments with us."

"It is still going down," remarked Jack, as he saw the red column drop
down past the thirty mark.

"Below freezing," added Mark.

The spirits fell in the tube until they touched twenty-eight degrees,
and there they remained.

"Twenty-eight degrees," remarked Professor Henderson. "That isn't so
bad. At least, we can stand that if we are warmly clad."