OcTOBER 12, 1916] 
_ THE investigation of the equations of motion of an 
aeroplane under the action of atmospheric disturbances 
such as gusts of wind is a problem to which attention 
was directed by Prof. Bryan in 1911 (‘Stability in 
Aviation,’” pp. 178-79, problems 4, 13). An attempt 
to solve this problem has now been made by Prof. 
Edwin Bidwell Wilson (S. Doc., 268, Sixty-fourth 
Cong., 1st sess.). The method adopted in this case 
consists in treating the disturbed motion as a forced 
oscillation, the disturbance being expressed in the 
form of an exponential function of the time. Unfor- 
tunately, however, it is not possible to obtain a 
simple solution of the problem in a symbolic form, 
and what Prof. Wilson has been able to do is to 
obtain numerical results for a particular aeroplane of 
which the values of the stability-coefficients have been 
determined experimentally. It will thus be necessary 
to repeat the calculations every time a new aeroplane 
is built. Prof. Wilson has for no adequate reason 
departed from the standard notation in his 
choice of axes. The problem with which he is dealing 
is only the two-dimensional case of longitudinal dis- 
turbances, and it is the universal custom in treatises 
both on pure and applied mathematics to choose x 
and y as co-ordinates in all two-dimensional problems. 
The same practice was followed in the earliest stability 
investigations both in England and abroad, and the 
difference of notation is bound to cause confusion. 
In a paper which appears in the August number of 
the Science Reports of the University of Seddai 
Messrs. Honda and Okubo arrive at an expression for 
the force on one of the elementary magnets of a group 
arranged in a space-lattice due to the presence of the 
other magnets of the group. From this, on calculat- 
ing the effect of an external field, they are able to 
obtain the magnetisation curve, and find it is identical 
with the well-known experimental curve. On varying 
the external field in the usual cyclic manner, the 
hysteresis loop is reproduced. It is then shown that 
the whole of the magnetic properties of magnetite can 
be reproduced on the theory that the elementary mag- 
nets constitute a cubic space-lattice, while those of 
pyrrhotine require a hexagonal lattice, as would be 
expected from its crystalline form. This molecular 
configuration for magnetite does not agree with that 
deduced by Bragg from the behaviour of the crystal 
towards X-rays. Finally, the authors show that the 
properties of ferromagnetic materials can be more 
completely and satisfactorily explained on the basis 
of the mutual action of elementary magnets than by 
the molecular field theory of Weiss. 
A RECENT publication of the U.S. Coast and Geo- 
detic Survey (Serial No. 23, Washington, 1916) gives 
the results obtained during 1913 and 1914 at the 
observatory near Tucson, Arizona. This observatory, 
which commenced operations in 1910, has a set of 
Eschenhagen magnetographs. The annual variation 
of temperature in the magnetograph chamber is about 
13° C., but the diurnal range is only about 0-19. Not- 
withstanding the favourable temperature conditions, 
the horizontal and vertical force magnetographs have 
given considerable trouble, large variations taking 
place in the scale values. The declination magneto- 
graph has worked more satisfactorily, and as three 
absolute declination observations are taken weekly, the 
results for that element should be especially trust- 
worthy. The Coast and Geodetic Survey has 
decided to .refer all observations of horizontal 
force to the so-called ‘international standard” 
of the Carnegie Institution of Washington. 
This entails the application of a correction of 
—23y(1y=1X10-*° C.G.S. unit) to previously published 
values of horizontal force at Tucson, and of a corre- 
NO. 2450, VOL. 98] 
NATURE 
115 
sponding correction to vertical force. Thus the mean 
annual values for earlier years printed in the present 
volume differ from those previously published. Opinions 
may differ as to whether this departure is not a little 
premature. Diurnal inequalities are given for the ten 
quietest days of each month and also for the five inter- 
national quiet days. Mean monthly values are given 
for both these sets of days, as well as for all days. 
The all-day mean in horizontal force, on the average 
of the twenty-four months of the two years, is about 
2-6 y below the other two means. Seven folding plates 
reproduce the magnetograms showing the chief dis- 
turbances of the two years. The largest disturbance 
in both years occurred in April, but no disturbances 
were of outstanding magnitude. The observatory also 
possesses a Bosch-Omori seismograph recording N.-S. 
and E.-W, components of seismic motion. The earth-’ 
quakes recorded are enumerated, and particulars are 
given of their principal features, but there is no 
information as to their epicentres. Much the largest 
disturbance recorded was that of March 30, 1914. 
Many engineers contend that the pressure over the 
teeth in modern high-speed gearing must be far from 
uniformly distributed, An interesting and new method for 
preventing any excessive concentration of the load on 
any part of the teeth is described in Engineering for 
October 6. The gearing was constructed by the 
General Electric Company of Schenectady, and used 
for coupling a high-speed steam turbine to a low-speed 
continuous-current generator. The wheels have double 
helical teeth, and the large wheel is built up of several 
comparatively thin discs, each separated from its 
neighbour by a small interval. The discs are bolted 
solidly together at their inner peripheries, but stand 
free from each other at their outer circumferences. 
Each disc has thus considerable axial flexibility, and 
if the load tends to be concentrated on any one of the 
discs, that disc bends axially, since the teeth are of the 
helical type. In this way the disc is relieved of the 
excess pressure, and a fairly uniform distribution of 
the load is secured. To enable the teeth to be cut on 
the rims of the discs, the discs are so made in the 
first instance as to be in contact also at the outer peri- 
pheries. The teeth can thus be milled without the 
discs springing, and after this operation is finished a 
narrow cut is made between the discs so as to obtain 
the required axial flexibility. 
A SHILLING edition of Sir Ray Lankester’s well- 
known and deservedly popular ‘‘ Science from an Easy 
Chair "’ has been published by Messrs. Methuen and 
Co., Ltd. This is the ninth edition of the book, which 
was first published in April, 1910, and reviewed in our 
issue of July 14 of that year (vol. Ixxxiv., p. 37) 
A FRENCH translation of Prof. F. Soddy’s monograph 
on the chemistry of the radio-elements, published in 
1912, has been made by M. E. Philippi, and is issued 
by MM. Gauthier-Villars and Co., in Paris, under the 
title ‘‘La Chimie des Eléments Radioactifs."” The 
price of the volume is 5 francs. 
Tue Wireless Press, Ltd., will shortly publish ‘‘ The 
Measurement of Capacity and Inductance,” by W. H. 
Nottage, illustrated, and a new and enlarged edition 
of ‘‘Elementary Principles of Wireless Telegraphy,” by 
R. D. Bangay. 
THE recently issued announcement list of the J. B. 
Lippincott Company includes the following new books 
and new editions :—‘t Shakespeare and Precious Stones,”’ 
Dr. G. F. Kunz, illustrated: the work will treat of 
all the known references to precious stones in Shake- 
speare’s works, with comments as to the origin of 
his material, the knowledge of the poet concerning 
