AIR CURRENTS IN RELATION TO AVIATION 365 



Conditions of Safety of Floaters and Fliers 



In taking up the question of the conditions of safety I shall 

 deal only with that part of the subject which is concerned with 

 the meteorologist's discretion and not with the airman's valour. 

 I could perhaps have made myself more clear by selecting 

 as title " The Dangers of Floaters and Fliers " ; but even that 

 title would not have been exact, because there is really no 

 danger in a line-squall or a cliff eddy if you have the skill to 

 recognise its approach and the discretion to keep out of its way. 



One distinction between floaters and fliers is an obvious one. 

 No harm can come to a drifting open boat except from waves, 

 whirlpools or the bottom. A floating balloon seems at first 

 sight to be immune from any sort of injury, so long as it does 

 not come to land. There are, as we have seen, the irregular 

 waves of gustiness to which the balloon cannot instantaneously 

 respond and consequently it must be subject to some stresses ; 

 but experience shows that they are not of great importance. It 

 is a little surprising that no one has yet made a machine to take 

 power out of the gustiness of the wind, using the variations 

 of velocity to drive a pump instead of the average velocity. It 

 is obvious that a mechanism could be made to pump water by 

 the gustiness of the wind and it would be very interesting to 

 know what sort of work an apparatus of the kind would show 

 in a balloon. I have seen no notice of any effect of gustiness on 

 the motion of a balloon and we may say that the " waves " 

 of our anemometric records are not a danger to a floater. 



It might appear indeed as though a floater would travel 

 serenely along and carry its own weather with it. If it starts 

 with a cloud it might travel with it as though the cloud were a 

 sort of umbrella ; if it is raining or snowing the balloon might 

 be expected to travel with the rain or the snow ; if it does not 

 there must be some complication of the structure of the atmo- 

 sphere giving a different regime of weather in the upper air 

 from that of the current in which the balloon floats. The con- 

 sideration of the immunity of a floater from the incidents of 

 weather, as experienced at a point of the fixed earth, is of some 

 practical importance in modern aerial navigation, because an 

 airship can at any time become a floater and drift with the air 

 current that supports it. I have therefore been curious to find 

 out whether a line-squall, which may set up a sort of destructive 



