RENNIE, JOHN, a celebrated
civil engineer, was the youngest son of a respectable farmer at Phantassie,
in East Lothian, where he was born, June 7, 1761. Before he had attained his
sixth year, he had the misfortune to lose his father; his education,
nevertheless, was carried on at the parish school (Prestonkirk) by his
surviving relatives. The peculiar talents of young Rennie seem to have been
called forth and fostered by his proximity to the workshop of the celebrated
mechanic, Andrew Meikle, the inventor or improver of the thrashing-machine.
He frequently visited that scene of mechanism, to admire the complicated
processes which he saw going forward, and amuse himself with the tools of
the workmen. In time, he began to imitate at home the models of
machinery which he saw there; and at the early age of ten he had made the
model of a wind-mill, a steam-engine, and a pile-engine, the last of which
is said to have exhibited much practical dexterity.
At twelve, Rennie left
school, and entered into the employment of Andrew Meikle, with whom he
continued two years. He then spent two years at Dunbar, for the purpose of
improving his general education. So early as 1777, when only sixteen years
of age, his Dunbar master considered him fit to superintend the school in
his absence, and, on being removed to the academy at Perth, recommended
Rennie as his successor. This, however, was not the occupation which the
young mechanician desired, and he renewed his former labours in the workshop
of Andrew Meikle, employing his leisure hours in modelling and drawing
machinery. Before reaching the age of eighteen, he had erected two or three
corn-mills in his native parish; but the first work which he undertook on
his own account was the rebuilding of the flour-mills at Invergowrie, near
Dundee.
Views of an ambitious kind
gradually opened to him, and, by zealously prosecuting his professional
labours in summer, he was enabled to spend the winter in Edinburgh, where he
attended the lectures of professor Robison on natural philosophy, and those
of Dr Black on chemistry. Having thus fitted himself in some measure for the
profession of an engineer, he proceeded to Soho, with a recommendation from
Robison to Messrs Bolton and Watt. On the way, he examined the aqueduct
bridge at Lancaster, the docks at Liverpool, and the interesting works on
the Bridgewater canal. At Soho, he was immediately taken into employment,
and it was not long ere Mr Watt discovered the extraordinary talents of his
young assistant. In the erection of the Albion mills in London, which was
completed in 1789, Mr Rennie was intrusted by his employers with the
construction of the mill-work and machinery, which were admitted to be of
superior excellence. These mills consisted of two engines, each of fifty
horse power, and twenty pairs of millstones, of which twelve or more pairs,
with the requisite machinery, were constantly kept at work. In place of
wooden wheels, so subject to frequent derangement, wheels of cast-iron, with
the teeth truly formed and finished, and properly proportioned to the work,
were here employed; the other machinery, which used to be made of wood, was
made of cast-iron in improved forms. This splendid establishment, which Mr
Watt acknowledges to have formed the commencement of the modern improved
system of mill-work, was destroyed in 1791, by wilful fire, being obnoxious
to popular prejudices, under the mistaken supposition of its being a
monopoly. The mechanism, however, established Mr Rennie’s fame, and he soon
after began to obtain extensive employment on his own account.
The earlier years of his
professional life were chiefly spent in mill-work; and his merits in this
line may be briefly stated. One striking improvement was in the bridge-tree.
It was formerly customary to place the vertical axis of the running
mill-stone in the middle of the bridge-tree, which was supported only at its
two extremities. The effect of this was that the bridge-tree yielded to the
variations of pressure arising from the greater or less quantity of grain
admitted between the mill-stones, which was conceived to be an useful
effect. Mr Rennie, however, made the bridge-tree perfectly immovable, and
thus freed the machinery from that irregular play which sooner or later
proves fatal to every kind of mechanism. Another improvement by Mr Rennie
has been adverted to in the above account of the Albion mills; but the
principal one was in the comparative advantage which he took of the water
power. He so economized the power of water as to give an increase of energy,
by its specific gravity, to the natural fall of streams, and to make his
mills equal to fourfold the produce of those, which, before his time,
depended solely on the impetus of the current.
Mr Rennie was gradually
attracted from the profession of a mechanician to that of an engineer. In
the course of a few years after his first coming into public notice, he was
employed in a considerable number of bridges and other public works, all of
which he executed in a manner which proved his extraordinary genius. His
principal bridges are those of Kelso, Leeds, Musselburgh, Newton-Stewart,
Boston, and New Galloway. The first, which was erected between 1799 and
1803, has been greatly admired for its elegance, and its happy adaptation to
the beautiful scenery in its neighbourhood. It consists of a level road-way,
resting on five elliptical arches, each of which has a span of seventy-three
feet, and a rise of twenty-one. The bridge of Musselburgh is on a smaller
scale, but equally perfect in its construction. A remarkable testimony to
its merits was paid in Mr Rennie’s presence, by an untutored son of nature.
He was taking the work off the contractor’s hands, when a magistrate of the
town, who was present, asked a countryman who was passing at the time with
his cart, how he liked the new bridge. "Brig," answered the man, "it’s nae
brig ava; ye neither ken whan ye’re on’t, nor whan ye’re aff’t" It must be
remarked that this bridge superseded an old one in its immediate
neighbourhood, which had a very precipitous road-way, and was in every
respect the opposite of the new one.
Mr Rennie was destined,
however, to leave more splendid monuments of his talents in this particular
department of his profession. The Waterloo bridge across the Thames at
London, of which he was the architect, would have been sufficient in itself
to stamp him as an engineer of the first order. This magnificent public work
was commenced in 1811, and finished in 1817, at the expense of rather more
than a million of money. It may safely be described as one of the noblest
structures of the kind in the world, whether we regard the simple and chaste
grandeur of its architecture, the impression of indestructibility which it
forces on the mind of the beholder, or its adaptation to the useful purpose
for which it was intended. It consists of nine equal arches, of 127 feet
span; the breadth between the parapets is 42 feet; and the road-way is
perfectly flat. Mr Rennie also planned the Southwark bridge, which is of
cast. iron, and has proved very stable, notwithstanding many prophecies to
the contrary. The plan of the new London bridge was likewise furnished by
him; but of this public work he did not live to see even the commencement.
Among the public works of
different kinds executed by Mr Rennie may be mentioned;—of canals, the
Aberdeen, the Great Western, the Kennet and Avon, the Portsmouth, the
Birmingham, and the Worcester;—of docks, those at Hull, Leith,
Greenock, Liverpool, and Dublin, besides the West India docks in the city of
London;—and of harbours, those at Berwick, Dunleary, Howth, Newhaven, and
Queensferry. In addition to these naval works, he planned various important
improvements on the national dockyards at Plymouth, Portsmouth, Chatham, and
Sheerness; and the new naval arsenal at Pembroke was constructed from his
designs. But by far the greatest of all his naval works was the celebrated
breakwater at Plymouth. It is calculated that he planned works to the amount
of fifty millions in all, of which nearly twenty millions were expended
under his own superintendence.
Mr Rennie died, October 16,
1821, of inflammation in the liver, which had afflicted him for some years.
By his wife, whom he married in 1789, he left six children, of whom the
eldest, Mr George Rennie, followed the same profession as his father. This
eminent man was buried with great funeral honours, in St Paul’s cathedral,
near the grave of Sir Christopher Wren.
The grand merit of Mr Rennie
as an engineer is allowed to have been his almost intuitive perception of
what was necessary for certain assigned purposes. With little theoretical
knowledge, he had so closely studied the actual forms of the works of his
predecessors, that he could at length trust in a great measure to a kind of
tact which he possessed in his own mind, and which could hardly have been
communicated. He had the art of applying to every situation where he was
called to act professionally, the precise form of remedy that was wanting to
the existing evil,—whether it was to stop the violence of the most
boisterous sea—to make new harbours, or to render those safe which were
before dangerous or inaccessible—to redeem districts of fruitful land from
encroachment by the ocean, or to deliver them from the pestilence of
stagnant marsh--to level hills or to tie them together by aqueducts or
arches, or, by embankment, to raise the valley between them—to make bridges
that for beauty, surpass all others, and for strength seem destined to last
to the latest posterity—Rennie had no rival. Though he carried the desire of
durability almost to a fault, and thus occasioned more expense, perhaps, on
some occasions, than other engineers would have considered strictly
necessary, he was equally admired for his conscientiousness in the
fulfilment of his labours, as for his genius in their contrivance. He would
suffer no subterfuge for real strength to be resorted to by the contractors
who undertook to execute his plans. Elevated by his genius above mean and
immediate considerations, he felt in all his proceedings, as if he were in
the court of posterity: he sought not only to satisfy his employers, but all
future generations.
Although Rennie did not
devote himself to the acquisition of theoretical knowledge, excepting to
that general extent which is required by every well-informed engineer, he
was fond of those investigations of a mixed character, where the results of
experiment are combined by mathematical rules, and a train of inquiry
directed and modified by the lights of theory. In his instrument for
ascertaining the strength of flowing water, he has made a contribution to
science of no small importance.
In person, Mr Ronnie was
greatly above the usual size. His figure was commanding, and his features
massive and strong, but with a mild expression. He was endeared to all who
knew him by the gentleness of his temper; and the cheerfulness with which he
communicated the riches of his mind, and forwarded the views of those who
made useful improvements or discoveries in machinery, procured him universal
respect. |