In our own day a striking proof of the same thing was given in the great fire in Tooley street, when Braidwood lost his life.  I witnessed that conflagration for a time from London Bridge, and its fury was something not to be described.  There were vaults under some of the warehouses stored with inflammable materials, the contents of which caught fire and burnt for a fortnight, defying all attempts to put them out.  Yet these very vaults, though they were blazing furnaces for all that time, were not materially injured.  When the warehouses came to be reinstated, it was only found necessary to repair and repoint them a little, and they were retained in use.  The fact is that the bricks have been calcined already, so has the lime in the mortar, and the sand is not affected by heat, so there is nothing in brickwork to burn.  Against each of these good qualities, however, we may set a corresponding defect.

If brickwork is easily thrown into any shape, it is also easily thrown out of shape.  It has little coherence or stability, less than masonry and very considerably less than timber.  If any unequal settlement in the foundation of a brick building occurs, those long zigzag cracks with which we in London are only too familiar set themselves up at once; and if any undue load, or any variation in load, exists, the brickwork begins to bulge.  Any serious shock may cause a building of ordinary brickwork to collapse altogether, and from time to time a formidable accident occurs owing to this cause.  The fact is, the bricks are each so small compared to the mass of the work, and the tenacity or hold upon them of even fairly good lime mortar is so comparatively slight, that there is really but little grip of one put upon another.

Persons who have to design and construct brick buildings should never forget that they have to be handled with caution, and are really very ticklish and unstable.  One or two of the methods of overcoming this to some extent may be mentioned.  The first is the introduction of what is called bond.  At the end of the last century it was usual to build in, at every few feet in height, bond timbers, which were embedded in the heart of the walls.  If these had always remained indestructible, they would no doubt have served their purpose to some extent.  Unfortunately, timber both rots and burns, and this bond timber has brought down many a wall owing to its being destroyed by fire, and has in other cases decayed away, and caused cracks, settlements, and failures.

The more modern method of introducing a strong horizontal tie is to build into the wall a group of bands of thin iron, such as some sorts of barrels are hooped with—­hence called hoop iron.  The courses of bricks where this occurs must be laid in cement, because iron in contact with cement does not perish as it does in contact with mortar.