24 AMID THE HIGH HILLS 
I have examined the evidence contained in the 
valuable and interesting correspondence mentioned 
above, and have also obtained all the information 
I could get elsewhere from books of authority and 
persons who have had special opportunities of 
observation. At the present day a valuable and 
novel class of evidence is available — that of 
observers in aeroplanes. Upon all the material 
thus obtained I have tried to form an impartial 
opinion. 
There appear to me to be four points to be 
borne in mind before arriving at any conclusion 
as to which bird is the quickest in flight, and the 
maximum speed of which each bird is capable. 
Emphasis is laid on the first three of the follow- 
ing points in some of the letters in the corre- 
spondence above referred to, but I think that the 
fourth point is of at least equal importance. 
1. Ground speed must be distinguished from 
air speed. 
2. The path of flight must be horizontal. 
3. There must be something to show that the 
bird is flying at its maximum speed. 
4. There must be a standard length of flight 
to which the test is to be applied. 
