Around-the-world flyers, even the most recent, have all flown more or less northerly routes, not following the equatorial belt, which is, as we all know, the earth's greatest circumference.  It is this course that our four young heroes take in Sky-Bird II, a plane designed and constructed by themselves, containing many features that aeronautics now takes for granted, and some not yet realized, which are, nevertheless, "within the scope of mechanical science," as Fraser says.