The principal disadvantages would seem to be:
1. The resistance of the gas-bag.
2. Danger of fire from close combination of petroleum motor and gas-containing envelope.
3. Danger of fire from self-electrification of surface.
4. Difficulties in the way of applying the propulsive screws in the most effective position.
5. Difficulties of making gas envelope gas-proof.
6. Great cost of airships.
7. The great amount of personnel needed for the manipulation of large airships.
8. Great liability of being destroyed by aëroplanes in war.
9. Insufficient power of quickly rising.