News from the Magazines. 
209 
short, the second longer than the seventh, but the longest of 
all are the fourth and fifth. When the wing is spread, as in 
soaring flight, these seven primaries form a remarkable series 
of slots, giving a perfectly graded echelon formation, which, 
when seen with the wing on the eye -level, appear as a series 
of steps, the slot between the first and second primaries being 
nearer the bird’s body and higher up than that between the 
second and third and so on. In this way, the air passing 
over a large area of the wing towards the tip, comes under the 
influence of a series of slots, which prevents eddies occurring 
and ensures maximum lift at high angles of incidence. 
Now watch the Chough as it swings round in a magnificent 
sweep into the wind. The tail is depressed and fanned on 
one side to catch the air and turn the bird much as a rudder 
turns a ship, while the primary feathers automatically spray 
out like the fingers on the hand, and with no apparent effort the 
bird is lifted 50 ft. or more into the air ! The angle of 
incidence of the wing at this moment is very large — almost it 
appears at times to be nearly 30 deg. or 35 deg., as far as one 
can judge through glasses — an angle which is far past ‘ stalling ’ 
on an uncontrolled wing. But the multiple slots control the 
stall, and the bird carries on with only a very slight movement 
of the control surfaces of the slotted wing, gaining altitude 
quite effortlessly, until in a few minutes it is soaring with 
others of its kind above the 5,000 foot peaks around. 
But these slots also play an important part, too, in helping 
to prevent the second cause of loss of lift in a wing, namely, 
air-spill.’ Obviously, the broader the tip of a wing, the 
greater the area over which the air can spill, and hence the 
greater the loss in lift due to this cause. If, however, the 
tip of the wing be broken up into a series of slots, as is the case 
with birds whose primaries separate in flight, the area 
over which air-spill can occur is greatly reduced, giving 
added efficiency in the way of lift. 
Hence the wide-spread primaries at the wing tips of the 
Chough, with their resultant slots, are Nature’s way of 
eliminating two defects well known in aeronautics, and 
account for the fine soaring powers of this and many other birds. 
The Vasculum for May contains especially two interesting articles on 
the ‘ Pearl Mussel in Hard and Soft Water,’ by Professor A. E. Boycott 
and on ‘ Duckweeds,’ by Dr. R. Blackburn. There are also shorter 
articles on ‘ A Reconstruction of Berwick Castle,’ by J. E. Hull, and on 
‘ Mimicry and Ventriloquy among Birds,’ by R. Craigs. 
The New Phytologist for June contains articles on the ‘ Radial Growth 
of Xylem and the Starch Reserves of Pinus sylvestris , ’ by W. Wight, and 
The Role of Organic Acids in Plant Metabolism,’ by T. A. Bennet-Clark . 
T. M. Harris describes a new member of the fossil Caytoniales and Lewis 
Knudson gives details of the non-symbiotic development of seedlings of 
Calluna vulgaris in pure culture. 
1933 Sept. 1 
