a ae Pe 
several days in advance. 
device. 
JANUARY. 29, 1914] 
NATURE 
609 
However, any further ex- 
penditure of public money should not be granted, un- 
less the information thereby obtained be published in 
such a detailed form and at such a price that.it would 
be available for the study of all who take an interest 
in meteorological science. R. M. Destey. 
Abbeyfield, Salisbury Avenue, Harpenden. 
Liquid Air as a Fixative. 
Last year when Mr. Atkins and I were searching 
for a method of extracting sap unchanged from 
various vegetable tissues, treatment with liquid air 
suggested itself and proved a valuable means _ for 
attaining this object. The rapidity of its action in 
suspending vital processes and chemical changes and 
in rendering protoplasm permeable, suggested its 
further application as a fixative. Since then most 
promising results have been obtained in various cells 
and tissues by Miss E. S. Marshall, working in this 
laboratory, showing various nuclear and cytoplasmic 
structures-with great clearness and with a complete 
absence of plasmolysis. Henry H. Dixon. 
School of Botany, Trinity College, Dublin. 
Atomic Models and X-Ray Spectra. 
Ir seems scarcely possible that Prof. Nicholson 
(NATURE, vol. xcii., p. 583) requires his two rings of 
electrons, rotating under the inverse square law, to 
have one and the same angular velocity; because, if 
so, the impossibility of two different radii is self- 
evident; but his letter does not guard against this 
elementary misapprehension. OLIVER LopGeE. 
Mariemont, Edgbaston, January 24. 
AUTOMATIC AEROPLANE CONTROLS. 
Ne interest has been excited in the an- 
nouncement contained in the daily Press 
that Mr. Orville Wright has succeeded in fitting 
aéroplanes with a device which, according to his 
statements, renders them as nearly “fool-proof ” 
as anything can be. 
This device, as illustrated in the Daily Mail, 
is an absolutely simple one, and works by com- 
pressed air. Lateral control is effected by a 
pendulum which operates an air valve, by which 
the compressed air is admitted to a cylinder 
containing a piston connected with the warping 
For longitudinal control, Mr. Wright 
uses a flat vane, which rises or falls when the 
air impinges on its under or upper surface; and 
this is similarly made to operate the elevator. 
The compressed air is generated by a small 
windmill, which will continue to work when the 
engines are stopped. 
I have pointed out in Nature, vol. xci., 
p- 556, that a pendulum, operating on the 
controlling devices of an aéroplane, instead of 
increasing the stability and damping out the 
oscillations, may produce the reverse effect. 
It is thus evident that there must be definite 
conditions under which such a: device as this 
may be able to accomplish its object, and 
that there are equally definite conditions under 
which it may lead to disastrous accidents. The 
inference is that Mr. Wright has by experimental 
tests arrived at a result which satisfies the ‘con- 
NO. 2309, VOL. 92] 
ditions favourable for automatic control as op- 
posed to those favourable for automatic wreckage. 
Apart from the use of a vane for longitudinal 
control, and a windmill as a generator of com- 
pressed air, the invention seems to differ very 
little from a patent previously claimed by Mr. 
H. G. Seager, of Colwyn Bay, which I have rather 
carefully examined, because I am interested in 
it, and he lives near. Seager uses a pendulum 
and air pressure, but instead of one he has eight 
valves, and the same number of cylinders: or 
pneumatics, with the result that he can place his 
warping devices or elevators in eight different 
positions, according to the strength and sense of 
the disturbance requiring to be counteracted. It 
thus represents a more elaborate control. 
There is a good deal of confusion at the present 
time as to what is meant by stability in aviation, 
and for this reason ‘‘automatic control’? would 
probably be a safer name than ‘automatic sta- 
bility” for self-righting devices involving move- 
able parts. The confusion arises largely from 
the want of an adequate theoretical basis of com- 
parison in the early days of aviation. Had theory 
preceded practice, the first experiments. would 
have soon disposed of the divergences - between 
them, which appear to be leading to endless con- 
troversies, misunderstandings, and mis-statements 
at the present time. ‘a 
Thus in a discussion on stability in The Aero- 
nautical Journal for October, recently’ issued, 
Mr, J. H. Ledeboer, near the end, says: “So 
far, everyone who has contributed to this dis- 
cussion appears to have made the cardinal mis- 
take of confusing stability with controllability, 
which are essentially different qualities, and are, 
in fact, often contradictory.” And in Mr. 
Berriman’s recent book, while introducing the 
term ‘“‘weathercock stability ” to designate some- 
thing which may or may not be synonymous with 
dynamical stability, he advances the opinion that 
an absolutely stable aéroplane would never vary 
its inclination to the horizon, and further that its 
centre of pressure would always coincide with its 
centre of gravity. So far from being absolutely 
stable, the last-named condition might theoretic- 
ally be described as giving neutral equilibrium, 
but unstable would be a more correct description. 
The success of the Wright device is described 
both by Wright himself and by his  fellow- 
passenger, Griffith Brewer. The statement that 
Wright flew several miles without touching the 
handles is undoubtedly genuine. 
While these things are happening in America, 
considerable interest is still being shown in this 
country in the Dunne machine, as is evidenced 
by the recent discussions before the Aéronautical 
Society. In this case an important feature is, that 
the tendency to excessive banking up in turning 
curves is counteracted by. making the angle of 
attack negative at the tions of the wings, so that 
these are really pressed downwards instead of 
lifted. The principle involved may be stated sym- 
bolically as follows, provided that we make the 
assumptions necessary to simplify the formule :-~ 
