Kent Scientists

The Barlows

Peter Barlow (1776-1862) - mathematician and scientist
Peter W Barlow (1809-85) - railway builder
William H Barlow (1812-1902)
- civil engineer  

A father and two sons from Woolwich


Peter Barlow

Peter Barlow

 by Samuel Cousins, after Sir William Boxall mezzotint, 1853 NPG D10588 © National Portrait Gallery, London

On 26th January 1843, distinguished scientists and other worthies assembled on the coastal downs between Folkestone and Dover to witness a bold and spectacular feat of engineering. Among them was the mathematician and physicist Professor Peter Barlow, of the Royal Military College at Woolwich. From a purpose-built pavilion they had a clear view of Round Down Cliff, 375 feet high, jutting out to sea, and unsuitable for tunnelling through. Eight tons of gunpowder had been packed into cavities created deep inside the cliff near its foot. At 2.26 pm a muffled rumble was heard and the ground shook as the gunpowder was electrically detonated, blowing out the foot of Round Down. Over the next two minutes the entire face of the cliff, a million tons of crumbling chalk, cascaded down into the sea. The final obstacle on the South Eastern Railway’s London to Dover route had been removed.

Barlow Wheel

Peter Barlow's Electric Wheel Motor, 1823

Peter Barlow was a mathematician and physicist. His long career in varied fields of research included two inventions which still bear his name. Barlow’s Wheel is a basic form of electric motor used by generations of science teachers to entertain their pupils and illustrate the principles of electromagnetism. The Barlow Lens is a component incorporated into telescopes and telephoto lenses to increase their magnification.

But it is in the field of railway engineering that the name of Barlow is particularly remembered. Railways were in their infancy, and their construction still relied a good deal on rule of thumb, but Peter Barlow’s rigorous experimenting helped provide practical data which future engineers could rely on. His investigations included the strength and best form of metal components, the layout of curves and gradients on the track, and aspects of locomotive design. But his greatest contribution to railway development was perhaps to bring up his two sons to be among the most eminent civil engineers of their generation.

In 1838 the newly-formed South Eastern Railway company began to construct its first line in Kent. Fifteen years later its tentacles had spread throughout the county. The man most closely involved in this rapid expansion was the Professor’s elder son Peter William Barlow. Thousands of Kent commuters still travel daily on the lines he built.

Born in Woolwich in 1809 and educated privately, P. W. Barlow learned his trade as a pupil of the engineer responsible for surveying the route for the South Eastern’s main line from London to Dover. Parliament had decreed that this should run via Reigate, Tonbridge, Ashford and Folkestone, and the surveyors’ task was to determine the best route, taking into account such factors as gradients and curves, and the need to deal with obstacles such as river crossings and hills that would require tunnelling.

P.W.Barlow's railways in Kent 

When construction began in 1838 P. W. Barlow was appointed Resident Engineer for much of the route, with day-to-day responsibility for all aspects of the job, including the construction of cuttings and embankments, bridges and tunnels, and the stations themselves. He went on to become the South Eastern’s engineer-in-chief, and oversaw the construction of other lines in Kent including the difficult route through the High Weald between Tonbridge and Hastings, completed in 1852. Among the surviving examples of Barlow’s work along this route are the 26-arch Colebrook Viaduct near Southborough, and no fewer than eight tunnels totalling three miles in length. (In several of these the contractor tried to get away with skimping on the lining. When this became apparent, additional layers of brickwork had to be inserted reducing the bore of the tunnels to the extent that to accommodate today’s rolling-stock the line has to narrow down to single track working through four of the tunnels.)

Thames tunnel entrance

Entrance to Barlow's Thames tunnel today, near the Tower of London

Later in his career P. W. Barlow was responsible for a tunnel under the Thames near Tower Bridge which still survives, though now only carrying cables and water pipes. To bore this tunnel he adopted an improved version of the ‘shield’ tunnel-boring technique first devised by Marc and Isambard Brunel. Barlow’s pupil, James Greathead, further developed the principle, and used it to excavate some of London’s deep underground (‘tube’) lines. A version of the Barlow-Greathead method is applied today in tunnel-boring around the world.

P. W. Barlow’s younger brother, William Henry, was if anything an even more distinguished engineer than his older sibling. Born and brought up in the environs of the Royal Military College in Woolwich, his long career combined wide-ranging research into engineering theory and practice with involvement with many of the iconic structures of Victorian engineering. His best-known monument is the vast arched roof of St Pancras station, which with a span of 243 feet was for a time the widest in the world. He was also involved in the design of the 1851 Crystal Palace and the completion of Clifton Suspension Bridge in Bristol after the death of Isambard Brunel.

W H Barlow

William Henry Barlow

W. H. Barlow served on the enquiry into the first Tay Bridge, whose catastrophic failure had cost at least 75 lives, concluding that the structure had been ‘badly designed, badly built, and badly maintained’. With his son Crawford he was responsible for its replacement, still standing as the longest railway bridge in country. He was involved in the design of the unique Forth Rail Bridge near Edinburgh and with large bridges in India and Australia, and also advised on urgently needed repair work to the cathedrals at Lincoln and Ely. Like his father and brother, he was elected a Fellow of the Royal Society.

At the age of ninety, Barlow’s interest in engineering was reported to be still ‘active and unabated’. He died in 1902 and is commemorated by a blue plaque on his home at 145 Charlton Road, Greenwich (formerly the home of William Congreve).