APRIL I, 1915] 
NATURE rai 

depends on the distance between them, and that in 
turn states a problem in shipbuilding which has never 
been solved satisfactorily, viz., the determination of 
the distribution of stress in way of an abrupt dis- 
continuity, such as a bridge, or other erection. In 
the absence of any theory to which complete assent can 
be given, we must turn to the record of experience. 
The author then proceeds to give descriptions and 
illustrative sketches showing typical cases of damage 
to existing ships at places of discontinuity. These 
examples are of particular value to engineers and 
others interested in the strength of materials, and will 
well repay careful study. 
An analysis of the damage observed supports certain 
conclusions which can be drawn from a consideration 
of the whole question of superstructures :—(1) That 
in way of a discontinuity in the structure of a ship, 
stresses outside the erection will be transmitted to the 
material of the deeper girder much more rapidly than 
has been thought to be the case; (2) that the fitting of 
expansion joints, spaced as in the present practice, 
does not appreciably relieve the superstructures of 
stress, or obviate damage; (3) the best method of pro- 
viding against damage in deckhouse superstructures 
is to dispose the material so as to make these capable 
of taking part in the straining action of the hull, 
following as far as possible the general law that all 
discontinuity of longitudinal material should be mini- 
mised. The author then proceeds to take certain 
typical cases, and gives methods of working out the 
scantlings required to comply with (3), above noted. 
Mr. F. W. Lanchester gave a contribution to the 
theory of propulsion and the screw propeller. The 
author made reference to the controversy in which 
Dr. Froude’s work was attacked violently by Prof. 
Henderson. Without entering, or taking part, in the 
dispute, Mr. Lanchester reviews the theory from its 
foundation, in order to make sure of his own ground. 
In the past there appears to have been insufficient 
attention to the initial definition of the problem, with 
corresponding uncertainty as to the ultimate interpre- 
tation of results. In discussing Dr. Froude’s theory, 
and speaking academically, Mr. Lanchester says that 
the wealx point of the whole conception is that there 
is no proof offered that either the work done (i.e. the 
energy expended), or the momentum communicated, 
is confined strictly to the column of fluid passing 
through the actuator, and there is, in fact, nothing 
to restrict, or confine, the fluid as in the case of the 
efflux theory, by which the problem is rendered really 
definite. It is understood that the régime contem- 
plated by Dr. Froude is not capable of exact expres- 
sion. This, however, is no obstacle to the application 
of any theory in real hydrodynamics; if it were neces- 
sary for the engineer to await the work of the pure 
mathematician in these matters, the subject would 
have made scarcely perceptible progress since the time 
of Noah. In such a case as the present, if the 
method of treatment contains 80 or 90 per cent. of 
truth, it may demand acceptance. 
Further work at the William Froude National Tank 
on the resistance of mercantile ship forms was pre- 
sented by Mr. J. L. Kent, and Mr. Stromeyer con- 
tributed an interestine paper on the law of fatigue 
applied to crankshaft failures. 

EAR PROTECTION AGAINST ARTILLERY 
SOUNDS. 
HOSE who have associated with our gunners 
must have noticed how often they suffer from 
deafness. The sudden access of pressure in the neigh- 
bourhood of a gun at the moment of firing imposes 
so great a strain on the drum of the ear that deafness 
is a usual result. The increase in pressure in the 
NO. 2370, VOL. 95] 


modern gun, and the high pressure still remaining 
when the shot reaches the muzzle, make the condi- 
tions more serious than they used to be comparatively 
recently. Not only those who are near the gun 
when fired, but those also in the neighbourhood of 
bursting shells, bombs, or explosives, are liable to 
suffer in a similar way even if they are not otherwise 
damaged. 
Mr. A. Mallock, F.R.S., who has for many years 
conducted investigations in connection with artillery, 
has invented an ‘tear defender,’ the object of which 
is to protect the drum of the ear from very sudden 
and violent access of pressure, while still allowing the 
minute variations produced by ordinary sounds to be 
received with but little loss. The defender consists 
of a containing piece made of ebonite and shaped like 
the pieces used in the game of Halma, and of about 
the same size. The ball end is very finely milled, 
and it is made to fit the passage of the ear, there 
being five sizes, differing very slightly in size in this 
part, to suit different people. The piece is pierced 
centrally by a hole 5 mm. in diameter at the small 
end, and gradually enlarging towards the other end, 
where it opens into a recess 1 cm. in diameter. Into 
this are fitted in order a flat ring washer, a disc of 
fine wire gauze, a very thin, flat ring washer, a deli- 
cate diaphragm, a very thin, flat ring washer, a disc 
of fine wire gauze, and a flat ring washer. When a 
pair of defenders are placed in the ears, the thin 
diaphragms, untouched except near their edges, 
where they are held, are free to take up aerial vibra- 
tion and to transmit it to the ear passage, and so the 
wearer hears ordinary sounds with but little loss; 
when, however, the violent impact due to gun fire or 
explosion in the neighbourhood occurs, the diaphragm 
is brought up against the wire gauze, by which it is 
prevented from further movement, thus limiting the 
increase of pressure in the air passage and defending 
the ear. 
The defenders are neatly packed in a small tin match- 
box with a rubber fitting, which prevents them from 
falling out, but which allows them to be removed at 
once. A small cleaning tool is similarly held elastic- 
ally so that it cannot fall out by accident. The price 
of the set is three shillings, and at the present time 
there is great scope for its use. The instrument is 
called the Mallock-Armstrong ear defender, and the 
address of the proprietors is 86 York Street, West- 
minster. Cy ViepBs 
SOME SCIENTIFIC ASPECTS OF 
PIANO-PLAYERS.1 
HERE are few modern inventions which have not 
been employed in the present war for the destruc- 
tion of property and of human life. The pneumatic 
piano-player is an exception. It is also exceptional in 
that it possesses but a scanty literature outside the 
catalogues of the manufacturers. It has never been 
associated with any inventor of distinction, and the 
general public knows nothing about its history. The 
aeroplane, on the other hand, is closely linked in 
popular thought, not only with such modern names 
as Wright, Langley, and Blériot, but also with the 
names of early designers and projectors of flying 
machines, such as Dante of Perugia and Leonardo da 
Vinci. Yet, considered merely from an engineering 
point of view, the modern piano-player is a marvel of 
human ingenuity. 
The feature which distinguishes it from its early 
predecessors is the element of controllability, which 
leaves the interpretation of the music largely to the 
1 Abridged from a discourse delivered at the Royal Institution on Friday, 
March 109, by Prof. G. H. Bryan, F.R.S. 
