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, both at home and abroad, it proved exceedingly remunerative.
Extensive works for the application of the process were erected at
Landore, where Siemens prosecuted his experiments on the subject with
unfailing ardour, and, among other things, succeeded in making a basic
brick for the lining of his furnaces which withstood the intense heat
fairly well.
The process in detail consists in freeing the bath of melted pig-iron
from excess of carbon by adding broken lumps of pure hematite or
magnetite iron ore. This causes a violent boiling, which is kept up
until the metal becomes soft enough, when it is allowed to stand to let
the metal clear from the slag which floats in scum upon the top. The
separation of the slag and iron is facilitated by throwing in some lime
from time to time. Spiegel, or specular iron, is then added; about 1
per cent. more than in the scrap process. From 20 to 24 cwt. of ore are
used in a 5-ton charge, and about half the metal is reduced and turned
into steel, so that the yield in ingots is from 1 to 2 per cent. more
than the weight of pig and spiegel iron in the charge. The consumption
of coal is rather larger than in the scrap process, and is from 14 to 15
cwt. per ton of steel. The two processes of Siemens and Martin are
often combined, both scrap and ore being used in the same charge, the
latter being valuable as a tempering material.
At present there are several large works engaged in manufacturing the
Siemens-Martin steel in England, namely, the Landore, the Parkhead
Forge, those of the Steel Company of Scotland, of Messrs. Vickers & Co.,
Sheffield, and others. These produced no less than 340,000 tons of
steel during the year 1881, and two years later the total output had
risen to half a million tons. In 1876 the British Admiralty built two
iron-clads, the Mercury and Iris, of Siemens-Martin steel, and the
experiment proved so satisfactory, that this material only is now used
in the Royal dockyards for the construction of hulls and boilers.
Moreover, the use of it is gradually extending in the mercantile marine.
Contemporaneous with his development of the open-hearth process, William
Siemens introduced the rotary furnace for producing wrought-iron direct
from the ore without the need of puddling.
The fervent heat of the Siemens furnace led the inventor to devise a
novel means of measuring high temperatures, which illustrates the value
of a broad scientific training to the inventor, and the happy manner in
which William Siemens, above all others, turned his varied knowledge to
account, and brought the facts and resources of one science to bear upon
another. As early as 1860, while engaged in testing the conductor of
the Malta to Alexandria telegraph cable, then in course of manufacture,
he was struck by the increase of resistance in metallic wires occasioned
by a rise of temperature, and the following year he devised a
thermometer based on the fact which he exhibited before the British
Association at Manchester. Mathiessen and others have since enunciated
the law according to which this rise of resistance varies with rise of
temperature; and Siemens has further perfected his apparatus, and
applied it as a pyrometer to the measurement of furnace fires. It forms
in reality an electric thermometer, which will indicate the temperature
of an inaccessible spot. A coil of platinum or platinum-alloy wire is
enclosed in a suitable fire-proof case and put into the furnace of which
the temperature is wanted. Connecting wires, properly protected, lend
from the coil to a differential voltameter, so that, by means of the
current from a battery circulating in the system, the electric
resistance of the coil in the furnace can be determined at any moment.
Since this resistance depends on the temperature of the furnace, the
temperature call be found from the resistance observed. The instrument
formed the subject of the Bakerian lecture for the year 1871.
Siemens's researches on this subject, as published in the JOURNAL OF
THE SOCIETY OF TELEGRAPH ENGINEERS (Vol. I., p. 123, and Vol. III., p.
297), included a set of curves graphically representing the relation
between temperature and electrical resistance in the case of various
metals.
The electric pyrometer, which is perhaps the most elegant and
original of all William Siemens's inventions, is also the link which
connects his electrical with his metallurgical researches. His invention
ran in two great grooves, one based upon the science of heat, the other
based upon the science of electricity; and the electric thermometer was,
as it were, a delicate cross-coupling which connected both. Siemens
might have been two men, if we are to judge by the work he did; and
either half of the twin-career he led would of itself suffice to make an
eminent reputation.
The success of his metallurgical enterprise no doubt reacted on his
telegraphic business. The making and laying of the Malta to Alexandria
cable gave rise to researches on the resistance and electrification of
insulating materials under pressure, which formed the subject of a paper
read before the British Association in 1863. The effect of pressure up
to 300 atmospheres was observed, and the fact elicited that the
inductive capacity of gutta-percha is not affected by increased
pressure, whereas that of india-rubber is diminished. The electrical
tests employed during the construction of the Malta and Alexandria
cable, and the insulation and protection of submarine cables, also
formed the subject of a paper which was read before the Institution of
Civil Engineers in 1862.
It is always interesting to trace the necessity which directly or
indirectly was the parent of a particular invention; and in the great
importance of an accurate record of the sea-depth in which a cable is
being laid, together with the tedious and troublesome character of
ordinary sounding by the lead-line, especially when a ship is actually
paying out cable, we may find the requirements which led to the
invention of the 'bathometer,' an instrument designed to indicate the
depth of water over which a vessel is passing without submerging a line.
The instrument was based on the ingenious idea that the attractive power
of the earth on a body in the ship must depend on the depth of water
interposed between it and the sea bottom; being less as the layer of
water was thicker, owing to the lighter character of water as compared
with the denser land. Siemens endeavoured to render this difference
visible by means of mercury contained in a chamber having a bottom
extremely sensitive to the pressure of the mercury upon it, and
resembling in some respects the vacuous chamber of an aneroid barometer.
Just as the latter instrument indicates the pressure of the atmosphere
above it, so the bathometer was intended to show the pull of the earth
below it; and experiment proved, we believe, that for every 1,000
fathoms of sea-water below the ship, the total gravity of the mercury
was reduced by 1/3200 part. The bathometer, or attraction-meter, was
brought out in 1876, and exhibited at the Loan Exhibition in South
Kensington. The elastic bottom of the mercury chamber was supported by
volute springs which, always having the same tension, caused a portion
of the mercury to rise or fall in a spiral tube of glass, according to
the variations of the earth's attraction. The whole was kept at an even
temperature, and correction was made for barometric influence. Though of
high scientific interest, the apparatus appears to have failed at the
time from its very sensitiveness; the waves on the surface of the sea
having a greater disturbing action on its readings than the change of
depth. Siemens took a great interest in this very original machine, and
also devised a form applicable to the measurement of heights. Although
he laid the subject aside for some years, he ultimately took it up
again, in hopes of producing a practical apparatus which would be of
immediate service in the cable expeditions of the s.s. Faraday.
This admirable cable steamer of 5,000 tons register was built for
Messrs. Siemens Brothers by Messrs. Mitchell & Co., at Newcastle. The
designs were mainly inspired by Siemens himself; and after the Hooper,
now the Silvertown, she was the second ship expressly built for cable
purposes. All the latest improvements that electric science and naval
engineering could suggest were in her united. With a length of 360
feet, a width of 52 feet, and a depth of 36 feet in the hold, she was
fitted with a rudder at each end, either of which could be locked when
desired, and the other brought into play. Two screw propellers, actuated
by a pair of compound engines, were the means of driving the vessel, and
they were placed at a slight angle to each other, so that when the
engines were worked in opposite directions the Faraday could turn
completely round in her own length. Moreover, as the ship could steam
forwards or backwards with equal ease, it became unnecessary to pass the
cable forward before hauling it in, if a fault were discovered in the
part submerged: the motion of the ship had only to be reversed, the
stern rudder fixed, and the bow rudder turned, while a small engine was
employed to haul the cable back over the stern drum, which had been used
a few minutes before to pay it out.
The first expedition of the Faraday was the laying of the Direct
United States cable in the winter of 1874 a work which, though
interrupted by stormy weather, was resumed and completed in the summer
of 1875. She has been engaged in laying several Atlantic cables since,
and has been fitted with the electric light, a resource which has proved
of the utmost service, not only in facilitating the night operations of
paying-out, but in guarding the ship from collision with icebergs in
foggy weather off the North American coast.
Mention of the electric light brings us to an important act of the
inventor, which, though done on behalf of his brother Werner, was
pregnant with great consequences. This was his announcement before a
meeting of the Royal Society, held on February 14, 1867, of the
discovery of the principle of reinforcing the field magnetism of
magneto-electric generators by part or the whole of the current
generated in the revolving armature--a principle which has been applied
in the dynamo-electric machines, now so much used for producing electric
light and effecting the transmission of power to a distance by means of
the electric current. By a curious coincidence the same principle was
enunciated by Sir Charles Wheatstone at the very same meeting; while a
few months previously Mr. S. A. Varley had lodged an application for a
British patent, in which the same idea was set forth. The claims of
these three inventors to priority in the discovery were, however,
anticipated by at least one other investigator, Herr Soren Hjorth,
believed to be a Dane by birth, and still remembered by a few living
electricians, though forgotten by the scientific world at large, until