and air currents going to the flame. An extremely high temperature is
thus obtained, and the furnace has, in consequence, been largely used in
the manufacture of glass and steel.

Before the introduction of this furnace, attempts had been made to
produce cast-steel without the use of a crucible--that is to say, on
the 'open hearth' of the furnace. Reaumur was probably the first to show
that steel could be made by fusing malleable iron with cast-iron. Heath
patented the process in 1845; and a quantity of cast-steel was actually
prepared in this way, on the bed of a reverberatory furnace, by Sudre,
in France, during the year 1860. But the furnace was destroyed in the
act; and it remained for Siemens, with his regenerative furnace, to
realise the object. In 1862 Mr. Charles Atwood, of Tow Law, agreed to
erect such a furnace, and give the process a fair trial; but although
successful in producing the steel, he was afraid its temper was not
satisfactory, and discontinued the experiment. Next year, however,
Siemens, who was not to be disheartened, made another attempt with a
large furnace erected at the Montlucon Works, in France, where he was
assisted by the late M. le Chatellier, Inspecteur-General des Mines.
Some charges of steel were produced; but here again the roof of the
furnace melted down, and the company which had undertaken the trials
gave them up. The temperature required for the manufacture of the
steel was higher than the melting point of most fire-bricks. Further
endeavours also led to disappointments; but in the end the inventor was
successful. He erected experimental works at Birmingham, and gradually
matured his process until it was so far advanced that it could be
trusted to the hands of others. Siemens used a mixture of cast-steel
and iron ore to make the steel; but another manufacturer, M. Martin,
of Sireuil, in France, developed the older plan of mixing the cast-iron
with wrought-iron scrap. While Siemens was improving his means
at Birmingham, Martin was obtaining satisfactory results with a
regenerative furnace of his own design; and at the Paris Exhibition of
1867 samples of good open-hearth steel were shown by both manufacturers.
In England the process is now generally known as the 'Siemens-Martin,'
and on the Continent as the 'Martin-Siemens' process.

The regenerative furnace is the greatest single invention of Charles
William Siemens. Owing to the large demand for steel for engineering
operations