AIR CURRENTS IN RELATION TO AVIATION 367 



the warm air in front of it. Thus we have the advancing 

 breaker of a bore and the way in which it can catch a balloon 

 is represented by the diagram (fig. 15). The first effect upon 

 the balloon is its elevation with the air which is being pushed 

 up; the second is the loading of the balloon with rain or snow ; 

 the third stage is the down-rush of the toppling crest which 

 falls earthward and produces the sudden squall that is charac- 

 teristic of some of these phenomena. But we must not forget 

 that our diagram only represents a part of the velocity of the 

 air in which the balloon was originally floating and that, besides 

 what is shown in the diagram, there is the velocity parallel to 

 the front which is suddenly arrested as the squall breaks and 

 the balloon finds itself in a region of very turbulent motion 

 which has actually caught it as it floats. 



(H-v). 



Waem 



1 

 "■9 



Fig. 15. — Illustrating the motion of air in the vertical section across the front 



of a line-squall. 



If this be a true description of the phenomena and all the 

 observations seem to confirm it, we must conclude that on the 

 approach of a line-squall there is no safety for an airship in 

 floating. It must run away if it can. It can run away success- 

 fully if it can travel at right angles to the line of the approaching 

 squall with a velocity half as great again as the normal com- 

 ponent of the surface wind. It must, however, be remembered 

 that the actual proportions of the velocities here mentioned are 

 hypothetical until we are fortunate enough, in some way or 

 other not yet clear, to obtain measurements which will enable 

 us to verify the explanation here suggested. 



When the balloonist is tired of the amusement of dropping 

 imaginary shells upon imaginary ships, we can find occupation 

 for his leisure in keeping an accurate log of the changes of 

 weather above a floater. 



