were introduced into each joint so as partly to be
lodged in one stone, partly in another, thus making it tolerably
certain that the rooms would be kept comfortable and dry in all
weathers. On the 30th of September the twenty-eighth course was
completely set. This and the next course received the vaulted floor,
which made the ceiling of the store-room and floor of the upper
store-room. For further security, therefore, there was a groove cut
round the upper surface of this course, in which was placed a circular
chain of great strength. Upon this chain, in the groove, was poured
melted lead, until the cavity was filled up. The next course was then
laid on, and this was also secured by a chain in like manner, it
being considered that the courses on which the floors rested demanded
every possible security. The formation of the floors, and the care
taken to avoid the danger of lateral pressure on the walls, is worthy
of notice. Each floor rested upon two courses; being firmly supported
by a triple ledge going circularly round the two supporting courses.
'Had each floor,' says the architect, 'been composed of a single
stone, this lying upon the horizontal bearings furnished by these
ledges, would, while it remained entire, have no lateral pressure or
tendency to thrust out the sides of the encompassing walls; and that
in effect the several pieces of which the floors were really composed
might have the same property as whole stones, the centre stone was
made large enough to admit of an opening, from floor to floor, to be
made through it; and being furnished with dove-tails on its four
sides, like those of the entire solid, it became the means by which
all the stones in each floor were connected together; and
consequently, the whole would lie upon the ledges like a single stone,
without any tendency to spread the walls. But if by the accident of a
heavy body falling, or otherwise, any of those stones should be
broken, though this might not destroy its use as a floor; yet the
parts would then exert their lateral pressure against the walls; and,
therefore, as a security against this, it became necessary that the
circle of the enclosing walls should be bound together, and the
building, as it were, _hooped_.' Thus assiduously did Smeaton urge
forward the work, yet without neglecting any of the necessary
precautions for its safety. By the 10th of October he had nearly
completed all the necessary arrangements for establishing a light