546 SCIENCE PROGRESS. 



one of a series of catastrophes which make it probable that 

 we may pay as dearly for conquering the air as we have 

 done in the past for ruling the waves. 



Probably no experiments have contributed so largely to 

 our knowledge of the conditions of balance and stability of 

 aerial machines as those initiated by Lilienthal, and which 

 have been brouo;ht to this sad termination. His work 

 fortunately survives, and among his disciples there is no 

 keener aeronaut than Mr. Percy S. Pilcher. On the other 

 side of the Atlantic much valuable work has been done in 

 the same direction by Mr. Octave Chanute, a former 

 President of the American Society of Civil Engineers. 



Remembering that the symmetrical form of all aerial 

 machines experimented on is sufficient to secure what might 

 be called their " transverse balance," the necessary condi- 

 tions are really threefold, viz., transverse stability, longi- 

 tudinal balance and longitudinal stability. It will, however, 

 be convenient to deal with the two last together. 



Transverse stability^ or stability for rolling motions, is 

 the only kind of stability which seriously affects the naval 

 architect, who knows that it can be secured, so far as small 

 displacements are concerned, by making a certain point 

 called the metacentre— whose position he can calculate 

 mathematically — above the centre of gravity of the ship. 

 In an aerial machine various factors affect the correspond- 

 ing kind of stability. 



According to our ordinary statical notions the stability 

 of any body in equilibrium can be increased by lowering its 

 centre of gravity. It might thus appear at first sight that 

 a soaring machine would be made more stable by bending 

 the wings upwards at the tips, by raising the aeroplane, or 

 by suspending a heavy weight considerably below the 

 machine. But every shipbuilder knows that if a vessel is 

 to sail steadily its centre of gravity must not be too far 

 below its metacentre, otherwise the ship will roll from side 

 to side in a heavy sea to a very inconvenient and even 

 dangerous extent. So our ships are built with only a very 

 small metacentric height; so small indeed that if the centres 

 of gravity were raised a foot or so higher than their actual 



