112 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Turbulent Motion. 
In the study which has been the subject of the foregoing pages we 
have always considered the motion of the air to he regulated by a dis- 
tribution of pressure balanced by the rotation of the earth, except in regard 
to the surface layer and one other suggested exception when the momentum 
of the general westerly circulation was invoked. It should here be noted 
that by this limitation to what may perhaps be called “ great circle motion,” 
we are considering almost exclusively the circulation above that half of 
the earth’s surface which is north of the northern tropic and south of the 
southern one. There is another section of meteorology which has to deal 
particularly with the region between the tropics where the beginnings of 
tropical revolving storms are to he found. These storms, which have 
a diameter of some hundred miles or more, as well as the tornadoes 
which have a diameter of perhaps a quarter of a mile, belong to the 
subject of turbulent motion, with which the eddies and whirls that are 
produced by obstacles on the surface of the ground are also associated. All 
these phenomena of turbulent motion, important as they sometimes are in 
real life and death, must be treated in a manner different from that of the 
present communication. 
(Issued separately March 23, 1914.) 
