Bomb-proof, the state of a roof strong enough to resist the shock 
of bombs falling upon it. With the enormous calibres now in use, 
it is almost impossible, and certainly as yet not worth while, to aim 
at absolute security from vertical fire for most buildings covered in 
bomb-proof. A circular vault 3'/, feet thick at the keystone, will 
resist most shells, and even a single 13-inch shell might not break 
through; but a second one could in most cases do so. Absolutely 
bomb-proof buildings are therefore confined to powder 
magazines, laboratories, &c., where a single shell would cause an 
immense explosion. Strong vaults covered over with 3 or 4 feet of 
earth, will give the greatest security. For common casemates the 
vaults need not be so very strong, as the chance of shells falling 
repeatedly into the same place is very remote. For temporary 
shelter against shells, buildings are covered in with strong balks 
laid close together and overlaid with fascines, on which some dung 
and finally earth is spread. The introduction of casemated 
batteries and forts, and of casemated defensive barracks, placed 
mostly along the inner slope of the rampart, at a short distance 
from it, has considerably increased the number of bomb-proof 
buildings in fortresses; and with the present mode of combining 
violent bombardments, continued night and day, with the regular 
attack of a fortress, the garrison cannot be expected to hold out 
unless effective shelter is provided in which those off duty can 
recover their strength by rest. This sort of buildings is therefore 
likely to be still more extensively apphed in the construction of 
modern fortresses. 

Written between September 29 and Oc- Reproduced from The New Ameri- 
tober 6, 1857 can Cyclopaedia 

Cyclopaedia, Vol. III, 1858