——— 
ON AERONAUTICAL PROBLEMS. 407 
Galileo and the Whale. 
20. It may seem that I have answered this question already, by the 
argument which I gave just now. And the man of conservative instincts, 
who objects to the building of giant airships as an unnecessarily dangerous 
adventure, seems at times to take his stand on these dimensional laws. 
I say ‘seems’, because his argument cannot in the nature of things be 
clear, since it is in fact erroneous: Galileo has another word to say, which 
effectively disposes of him too. 
We saw just now that Nature, confined to her materials of bone and 
muscle, seems to have exhausted her inventive powers in designing the 
elephant. It may have crossed your minds, as I was speaking, that I 
failed to take account of the whale. But Galileo saw, and drew attention 
to, the very different conditions which obtain when an animal, instead of 
fighting gravity on land, eludes its enemy by taking to the water. To 
quote Professor Thompson once again: *.. . if the animal be wholly 
immersed in water, . . . then the weight is counterpoised to the extent 
of an equivalent volume of water, and is completely counterpoised if the 
density of the animal’s body, with the included air, be identical (as in a 
whale it nearly is) with the water around. Under these circumstances there 
ts no longer a physical barrier to the indefinite growth in magnitude of the 
animal,’ 11 
Influence of Scale on the Strength of an Airship. 
21. Turning from zoology to aeronautics, we find here a reason for the 
fact that the airship has already left the aeroplane so far behind in the 
scale of size. The parallel is not exact, for reasons which I have 
not time to elaborate; but it is sufficiently exact for our purpose. 
Relying for its ‘lift’ upon its buoyancy, the airship experiences a rela- 
tively insignificant ‘ dimensional handicap’ in the stresses which it has 
to sustain,—whether these arise from the loads which it carries, or from the 
_ air forces which it encounters as it turns. By doubling every dimension, 
we obtain an airship which will carry eight times as much load, and can 
withstand winds of the same strength as before. 
Incidental Advantages of Size. 
22. Indeed, there is a certain advantage in respect of strength which 
comes from increased size. Suppose that we took an existing airship 
_(R.33 say) and decreased every dimension by two. According to dimen- 
sional theory it could still fly and it would have adequate strength ; but 
in reality its structure would have become impossibly flimsy. It is 
difficult to realise how slight the members are already : the total cross-section 
of all the duralumin girders used as longitudinal members of R.33 is only 
8 square inches! Divide this by four, and you would have material 
which the slightest corrosion would weaken almost to vanishing point. 
Conversely, by increasing the size, and employing material of stouter 
" gauge, we lessen the importance of corrosion as a factor in our calculations ; 
_ we render possible methods of construction which were not practicable 
11 Growth and Form, p. 21. 
