jULaa. 1915) 
than two tons of explosives could be carried, and 
this only at a low altitude. Naturally, other 
things being equal, the weight of the framework, 
etc., of a small airship is a larger proportion of 
the gross lift than the corresponding weight of 
a large airship. 
In that type of airship in which the walls of 
the gas-container are themselves the ‘‘frame- 
work” of the displacement body (the “non-rigid ” 
type), much weight is saved, but disadvantages 
come in that strains on the fabric affect its 
gas-tightness, which is also much affected by 
action of sun and other influences. 
Again, the attachment of the car (containing the 
engines, etc.) by wire ropes to the container is 
worked out on the assumption that the gas- 
container will retain its shape. This end is 
attained in single gas-containers by having a bag 
of air (the “ballonet’’) inside the container, into 
which is pumped air under pressure, to maintain 
the full volume and shape of the envelope. If, 
however, compartments are to be used in the 
container, some means of equalising their 
pressures even if one be ruptured must be 
devised, otherwise the shape will be distorted. 
This is no easy task. 
The non-rigid type has the great advantage of 
being quickly deflatable for transport packed 
up. Examples of this type are the Parseval and 
Astra-Torres, in which latter ship an ingenious 
system of suspension greatly strengthens the gas- 
container. 
The ‘semi-rigid ” type has some of the advan- 
tages and the disadvantages of both the other 
types. Examples are the Forlanini (Italian) and 
Astra XIII. (Russian). 
The material of which gas-containers are 
usually constructed is made of layers of cotton 
fabric cemented to layers of rubber. In order to 
intercept the blue (actinic) rays of light that 
“rot” the rubber very quickly and make it porous 
to the gas, the fabric is coloured yellow. Gold- 
beater’s skin makes a very gas-tight container, 
but 
” 
untreated is affected by rain, which is 
absorbed, and by its weight decreases the net 
lift. This disadvantage applies. to untreated 
fabrics, which are therefore usually varnished 
with an aluminium varnish, thus preventing water 
absorption and promoting gas-tightness. Fabric 
impregnated with gelatine, rendered flexible by 
added glycerine, and insoluble by formaldehyde, 
has given promising results. Oiled silk is very 
gas-tight but seams are troublesome. Very much 
research is still required into the question of 
fabrics. 
Propulsion demands a power plant and means 
for obtaining a reaction from the air. 
of power installed to weight lifted has been 
steadily rising both in airships and aeroplanes. 
The first Zeppelin airship (1900) weighed 10,200 
kilograms and the motors were two, totalling 
32 horse-power. Zeppelin III. (1906) lifted 
12,575 ke., and the motors (2). totalled 130 
effective h.p. The “L1” (marine) of 1913 lifted 
about 28,000 kg., and the motors totalled 720 
2383, VOL. 95| 
NO. 23 
The ratio | 
NATURE 

483 

h.p. As an indication of the performances that 
may be expected from airships in years to come, 
we may note the proportion of power to weight 
lifted in the last vessel as one horse-power to every 
80 Ib. lifted. The speed attained is fifty miles 
an hour. In the case of an aeroplane doing 
ninety miles an hour or so, the weight lifted is 
only about 15 lb. per horse-power. 
Screw propellers are universally used for air- 
ships, and are often of wood. They are usually 
placed at the sides of the gas-container in rigid 
vessels and below it in non-rigid vessels. Much 
research is needed as to the best position for 
propellers relatively to the body to which they are 
attached. 
A strong reason for increasing the power of 
airships is that by so doing a large amount of lift 
can be obtained by the dynamic action of the 
large control surfaces, which, by directing the 
airship’s nose up, are able to give it a very fast 
rate of rise, much quicker than that of aeroplanes. 
The maximum height attained by airships is 
somewhat more than 10,000 feet (Zeppelin and 
Italian). Aeroplanes have ascended twice as high 
and ordinary balloons three times as high. To 
attain 10,000 feet high an airship must sacrifice 
much ballast and gas, so that it cannot voyage 
for its longest period at a great height. Zeppelins 
are claimed to be capable of holding the air for 
three days, but not at full speed or height. There 
is no advantage in going very high (except 
for military reasons), and under 3000 feet 
would be a usual zone in which to operate were 
it not for anti-aircraft measures. Some day, 
when the airship is better developed, it may pay 
to go to great heights in order to obtain the 
advantage of lessened resistance to advancement 
due to the tenuity of the air. 
As regards steering and stability, it may be 
said at once that most airships steer clumsily 
and require large spaces in which to manceuvre. 
Our little non-rigid vessels have been specially 
developed for handiness in our much wooded 
country, but Zeppelins are craft for vast open 
spaces.. The dynamic stability of an airship is 
a complicated matter to work out. Besides 
ordinary pitching and rolling there are added 
effects due to surging of the gas and distortion 
of the gas-container. Propellers also complicate 
the stability question. Large control surfaces are 

essential, sticking well out from the body, to 
avoid its “wash.” 
A REGIONAL SURVEY.} 
MODERN element in the fascination that 
4 islands undoubtedly exert is their biological 
interest. What are the island’s inhabitants of 
high and low degree? How came they there and 
whence? How has the isolation affected them? 
1 “A Riological Survey of Clare Island in the County of Mayo, Ireland, 
and of the Adjoining District.” Section I. (comprising !’arts x to 16), Intro- 
duction, Archzology, Irish Names, Agriculture, Climatology. Geo'ogy, 
Botany. Section II. (comprising Parts 17 to 47). Zoology (Vertebrata, 
Mollasca, Arthropo: Polychzta). Section III. (comprising Parts 48 to 
68), Zceology (Oligochatta to Protozoa), Marine Ecolozy, Summary. 
(Dublin: Hodges, eee and Co., Ltd. ; London: Williams and Norgate, 
IQ1I-I5-) 
a 


