6o THE POPULAR SCIENCE MONTHLY 



wind is strong a landing should not be attempted in any such place. 

 If forced to land in a place of this kind the machine should be headed 

 along and not at right angles to the direction of the hill. 



4. Aerial Torrents. — Steep barren valleys, especially of clear still 

 nights and when the upper reaches are snow covered, are the beds of 

 aerial drainage rivers that at times amount to veritable torrents. There- 

 fore however quiet the upper atmosphere and however smooth its sail- 

 ing, it would be extremely dangerous to attempt to land an aeroplane 

 at such a place and such a time. 



Note 

 All the above sources of danger, whether near the surface like the 

 breakers, the torrents and the eddies, or well up like the billows and 

 the wind sheets, are less and less effective as the speed of the aeroplane 

 is increased. But this does not mean that the swiftest machine neces- 

 sarily is the safest; there are numerous other factors to be considered 

 and the problem of minimum danger, or maximum safety, if the aero- 

 naut insists, can only be solved by a proper combination of theory and 

 practise, of sound reasoning and intelligent experimentation. 



