The Sky-Bird II was now running straight ahead with the speed of the wind, John giving the craft more and more gas, and crowding her pretty close to the limit.  The wind swept by both sides of the streamlike cabin with a rushing sound like the distant roar of a huge cataract; the flexible window glass gave slightly to its pressure, but there was no sign of it breaking.  One minute they were in the midst of a cumulus cloud; the next, through it.  Now they saw the faint outline of the earth, now sky; now the earth was screened by cloud, but above were the blue heavens.