JOHN RENNIE

Imagination has been a hallmark of our species since the earliest times. Manifested in cave paintings to fashion a record or merely for the sheer pleasure of originality, and in stone tools that made life a little easier. England’s Stonehenge exemplifies our taste for structures, an enduring symbol of a persistent drive to modify our environment.

Later, as capabilities developed and wealth accumulated, our projects became grander. The Lighthouse of Alexandria, built 2,300 years ago, was an ambitious undertaking. Standing about 100 metres tall, its light would have been visible to seafarers up to 50 km away. While a useful aid to navigators, the structure was more: an unmistakable statement of the power and engineering prowess of the region’s Hellenic rulers. ‘Pride comes before a fall’ goes the biblical advice, attested here in the destruction of the tower by a series of earthquakes. Nevertheless, it stood for circa 1,000 years. Discussed in Jimbo’s Assumption when contemplating the life and deeds of Claudius Ptolemy, who aimed to illuminate the world, albeit through knowledge rather than light.

Our appetite for invention, design, construction, and manufacturing has grown ever since, driven by amalgams of ambition, altruism, economics, faith, greed, happenstance, and military imperatives. In Great Britain, a colossus of 19th century civil engineering was Thomas Telford, who left his mark with structures extant across the island and beyond. His endeavours are widely documented. A contemporary, sometimes a competitor, was the remorseless John Rennie, a lesser known but dedicated engineer.

Both were born into mid-18th century rural southern Scotland, but their early lives diverged markedly. For Telford, a Borders childhood of poverty mitigated by elementary education, then an apprenticeship as a stonemason, before escape to London and the commencement of a glittering career. Rennie’s family were prosperous farmers, thriving in the pastoral beauty of East Lothian on an estate named Phantassie, to the east of Edinburgh.

Fascinated by engineering, Rennie began working for a noted local millwright (now more commonly termed a mechanical fitter or machinery mechanic) as a twelve-year-old, while continuing, perhaps intermittently, to attend school. Despite his technical and commercial passions, the young man absorbed sufficient knowledge to enrol at Edinburgh University. He studied natural philosophy, now physics, for three years, in parallel with managing his own millwrighting business, repairing, maintaining, and upgrading machinery, providing a broad foundation of practical skills and scientific principles.

His professor, the accomplished John Robison, a polymath whose teaching encompassed astronomy, hydrodynamics, and electricity & magnetism, recommended Rennie to his friend, James Watt, who by then had an established reputation and a steam engine business in Birmingham. In 1784 CE, Rennie’s cooperation with Watt brought him to London to supervise an engine project at the Albion Flour Mill. Their relationship permitted Rennie to undertake contracts on his own account, which he quickly acquired. Commissions from flour mills, distilleries, and breweries accumulated, soon followed by sugar mills, marking his rapid ascent as an independent and sought-after engineer.

Rennie had come to London armed with several letters of introduction. These enabled him to extend his potential from machinery and steam technology into civil engineering. He accessed canal projects, undertaking surveys and project management across England, in Ireland, and back in his native Scotland. The Crinan Canal, a 14 km waterway, provided a shorter route for commercial and fishing vessels between the Glasgow industrial conurbation and the Inner Hebrides. Today, a heavily used leisure facility, unimaginable in Rennie’s era.

His ventures extended into water supplies, land drainage, lighthouses, breakwaters, and dockyards. The growth of the Royal Navy provided impetus for the latter. He advised on novelties including diving bells and steam-powered dredgers.

In parallel, he attained credence as a builder of bridges, the field that gained him a widespread reputation. An innovator, his bridges combined stonework with new cast-iron technology, allowing audacious creations with wide, low, elliptical arches. His aesthetic sense, hitherto dormant, became evident in edifices designed with an artistic sensibility, suggesting consideration of their impact on the landscape. An engineer, certainly, but now an architect?

Within his lineage of bridges were three over the Thames, all now replaced. One, Waterloo Bridge, is widely regarded as his masterpiece. It opened in 1817 CE, a granite structure almost 750 metres long, with nine arches separated by stone columns. Despite a reputation as a preferred location for suicide attempts, the bridge attracted accolades. Romantic artist John Constable’s portfolio depicts its opening. The Impressionist, Claude Monet, offered his interpretation of the bridge within a series of works. The Italian Neoclassical sculptor, Antonio Canova, designated it as “the noblest bridge in the world”.

Rennie’s subsequent London bridges were completed after his death in 1821 CE by his two sons, John and George, who would also carve out noteworthy careers as engineers, bolstering the Rennie family’s lasting impact on British engineering history.

Married with five surviving children, elected to the Royal Society, nationally recognised, John Rennie received a public funeral and burial in St Paul’s Cathedral, a final acknowledgement of a great engineer.

The closing words go to his biographer, Samual Smiles, in a summary that encapsulates the man and his monumental achievements: “Mr Rennie established a reputation for truthfulness, honesty, and uprightness…a man of powerful and equally balanced mind…calm, serene, and solid, like one of his own structures”.