¥.3.-2 
collect on the windward side of an island where the 
shore is bluff and play in the rising currents caused 
by the lift of the land. They undoubtedly employ 
these means in following the boats,but it may well be that 
this is not the whole story. It requires very little 
elevation in the course of the wind to enable a bird 
to soar upon it, for they are masters of the art. The 
whole truth will be learned sooner or later, I sup¬ 
pose, and meanwhile such careful observations as those 
of your paper will materially help. The carrying for¬ 
ward of the centre of gravity relative to the centre 
of Support as the force of the wind increases is theo¬ 
retically sound. To make the whole business scien¬ 
tifically clear, however, is more than anyone has yet 
accomplished, I believe. 
There are so many elements involved. There 
is the question of the form, the relations of sur¬ 
faces in space. The common anemometer owes its spinn¬ 
ing motion to the difference in effective pressure 
upon concurr and convex surfaces of equal projected 
area. Has this general fact an application? Then 
there is the question of possible reactions from one 
part of the surface upon other parts, as from the under¬ 
side of the wings up against the stern and tail, which 
