If they did not die of hunger, if they did not die of thirst, the reason would simply be that, in a few days, as soon as their gas was exhausted, they would die for want of air, unless indeed the icy cold had killed them beforehand! By this time, in fact, the temperature had become so exceedingly cold that a further encroachment on their little stock of gas could be put off no longer.

The light, of course, they could manage to do without; but a little heat was absolutely necessary to prevent them from freezing to death.

Fortunately, however, the caloric developed by the Reiset and Regnault process for purifying the air, raised the internal temperature of the Projectile a little, so that, with an expenditure of gas much less than they had expected, our travellers were able to maintain it at a degree capable of sustaining human life.
By this time, also, all observations through the windows had become exceedingly difficult.

The internal moisture condensed so thick and congealed so hard on the glass that nothing short of continued friction could keep up its transparency.

But this friction, however laborious they might regard it at other times, they thought very little of just now, when observation had become far more interesting and important than ever.
If the Moon had any atmosphere, our travellers were near enough now to strike any meteor that might be rushing through it.