482 

to the artillerist. The fact that the manufacturing 
process of an explosive like this is of the most 
delicate kind and has to be conducted with military 
precision, has been constantly overlooked; and 
at the present moment it is not too much to say 
that there is only one material available for 
modern gunnery, and that is cotton. 
PROBLEMS OF AIRSHIP DESIGN 
CONSTRUCTION, 
WHE problem of the airship falls naturally into 
three parts, concerned with flotation, pro- 
pulsion and steering respectively. The best 
results in any of these three branches are to a 
great extent antagonistic to similar success in 
one or both of the other two. For instance, 
flotation, which is purely a displacement problem 
at bottom, demands that the displacement body 
should have the greatest volume for the least 
superficies, i.e., that it should be spherical. 
Propulsion, on the other hand, demands that the 
body be of the shape having least head-resistance, 
i.e., of long fish-shape. Steering, with which is 
linked dynamic stability, demands that large fins 
and control surfaces be affixed to the body, which 
otherwise would set itself broadside on to the 
relative current caused by its forward movement. 
These auxiliary surfaces add to the weight, that 
AND 
is, oppose flotation and add to the head- 
resistance, thus opposing propulsion. Again, 
the displacement body must of necessity consist 
mainly of a gas lighter than air. All the light 
gases are highly inflammable (or if not have some 
other disadvantage), and consequently are danger- 
ous in proximity to an internal-combustion motor, 
such as is universally used for propulsion, as 
being the only motor with a good ratio of power 
to weight. Therefore the motor must not be 
placed too close to the gas-container, and in 
consequence it is difficult to enclose all the parts 
of the airship in a single “streamline” body of 
least resistance, and the head-resistance and 
weight are thus both increased considerably, 
opposing propulsion and flotation. 
The above list of incompatibilities might be 
extended considerably, as every airship designer 
knows to his cost. It is not to be wondered at, 
therefore, that airship design is in so fluid and 
embryo a condition that the future of the airship 
is looked upon as extremely dubious in many 
cuarters. The fact, however, that so much pro- 
gress has been made in face of stupendous difh- 
culties is a happy augury for the future of the 
airship, especially as many of the difficulties met 
with are due mainly to the fact that airships are 
at present small, and they will disappear as soon 
as experience and growing confidence enable 
large and larger vessels to be built. 
To deal with the displacement body, or lifting 
unit, first. The lift obtainable is, of course, 
directly proportional to the weight of air dis- 
placed and inversely proportional to the weight of 
the displacement body in itself. Roughly, 
thirteen cubic feet of air at sea-level and normal 
NO. 2383, VOL. 95] 
NATURE 

[JULY 1, 1915 
temperature weigh one pound, so that a lifting 
unit displacing that volume would lift one pound 
minus its own weight. Consequently, if the lift- 
ing unit consisted of “nothing shut up in a 
box”? as the schoolboy’s definition of a vacuum 
runs, only the weight of the box would have to 
be deducted from the gross lift obtainable. As 
no light vacuum-container could maintain its 
shape against atmospheric pressure, however, a 
gas must be used to keep the displacement body 
distended by its expansive properties. The gas 
universally used for airships is hydrogen. This 
weighs about one-fifteenth of unit volume of air, 
so that only 1/15 gross lift is lost by its use. The 
possibilities of getting wonderfully enhanced ‘ift 
by new gases, lighter than hydrogen, are thus 
seen to be illusory. 
Coal gas was long used (and still is) for ordin- 
ary spherical balloons, as being cheaper and more 
available than hydrogen, but being about ten 
times as heavy as hydrogen, is comparatively 
useless for airships. Ammonia vapour has been 
suggested for airships, as being non-inflammable, 
but is about eight times as heavy as hydrogen 
and of a destructive character to metal, ete. 
The provision of a stable non-inflammable light 
gaseous mixture would solve so many practical 
difficulties in the construction of airships that 
many thousands of pounds could profitably be 
expended in research on this problem. Failing 
this provision, all precautions must be taken to 
prevent fire, or to minimise its effects on board 
airships. 
Hydrogen being non-explosive apart from 
oxygen, can be isolated in containers jacketed 
with an inert gas and thus rendered harmless. 
The division of the displacement body of an air- 
ship into compartments is desirable from this 
and other points of view. For example, a large 
volume of gas in a thin fabric container is prone 
to surge about and strain the container when in 
motion. Compartments prevent this and also 
localise leakage due to rupture of any part of 
the container. 
The type of airship in which this principle is 
carried farthest is the rigid type (Zeppelin) in 
which the displacement body consists of seven- 
teen or eighteen separate gas-containers, set in 
a. rigid cylindrical framework, like peas in a pod. 
The chief advantages of the rigid framework are 
(i) that the actual gas-containers are relieved of 
strain and are (ii) protected from the influence of 
weather. The disadvantages are (i) the loss of 
gross lift due to the weight of the framework, 
and (ii) the fact that the airship cannot be folded 
up for transport or storage, and must con- 
sequently be housed in a large and expensive 
shed. 
The gross lift of a large Zeppelin is about 
twenty-five tons, of which about twenty tons are 
absorbed by the framework, engines, etc. This 
gives a net lift of only about one-fifth of the 
gross lift, a figure that could be much improved 
upon by making the vessel larger. This net lift 
has to account for crew, etc., so that not more 
