Upon Putney Heath, by the road-side, stands an obelisk, to record the
success of a discovery made in the last century, of the means of
building a house which no ordinary application of ignited combustibles
could be made to consume. The inventor was Mr. David Hartley, to whom
the House of Commons voted 2,500_l._, to defray the expenses of the
experimental building, which stood about one hundred yards from the
obelisk. In 1774, King George the Third and Queen Charlotte took their
breakfast in one of the rooms; while in the apartment beneath, fires
were lighted on the floor, and various inflammable materials were
ignited, to attest that the rooms above were fire-proof. Hartley's
secret lay in the floors being double, and there being interposed
between the two boards sheets of laminated iron and copper, not thicker
than tinfoil or stout paper, which rendered the floor air-tight, and
thereby intercepted the ascent of the heated air; so that, although the
inferior boards were actually charred, the metal prevented the
combustion taking place in the upper flooring.
Another experiment took place on the 110th anniversary of the great fire
of London, when a patriotic lord mayor and the corporation of London
witnessed the indestructible property of the structure. Yet, the
invention was never carried into further practice. The house was, many
years after, converted into a tasteful villa, although the obelisk
records the success of the experiment.
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