Bushy Hill, Essex

Although not an obvious tourist destination, Bushy Hill is the biggest landmark in the area of South Woodham Ferrers, Essex, and has played a notable role in the history of technology, as well as unintentionally providing natural science revelations.

From the 1950s, Bushy Hill was one of the sites used by Marconi for its radar development programme, and as a result of the prominence of this technology upon its summit, it has come to be known as “Radar Hill”. It is visible for miles around and commonly used as a navigation point for planes flying using Visual Flight Rules (VFR). Many people have therefore seen Bushy Hill, but few are aware of its interesting history.


Marconi Radar (pictured in 2006). This is one of the antennas at TQ8198 : Bushey Hill Radar near South Woodham Ferrers. Only a few short years ago the idea that Marconi would cease to exist except in name would have been unthinkable. ( © Copyright Glyn Baker, CC BY-SA 2.0)

The United Kingdom’s radar system had been rapidly run down towards the end of the Second World War, but the first Soviet nuclear test in 1949 and the beginning of the Korean War in 1950 gave a new urgency to improving air defences. Marconi won significant contracts to develop radar, and acquired the Bushy Hill site in the mid-1950s in order to carry out trials on proposed new radar technology.

Bushy Hill was selected because existing sites were “rather too good”: they were located in dips and depressions that insulated radars from noise (called “clutter” in radar terminology) caused by reflections of radar signals from unwanted sources such as the ground.* However, to improve radar performance, it was necessary to find a way of reducing clutter. Bushy Hill, with unobstructed 360˚ views, and conveniently close to the Chelmsford headquarters of Marconi radar, was the perfect site. A large, 75 feet wide antenna was installed, and used to develop a range of transmitters and signal processing systems which were sold all over the world.

Bushy Hill has a Type 80 aerial mount, which had revolutionised radar in 1953. Developed under an RAF programme with the curious title GREEN GARLIC, this system dealt with both early warning and controlling interceptions. These extra seconds of advance notice acquired greater significance with the 1955 development of the Soviet H-bomb and the existence of new supersonic bomber planes. In 1959, the Marconi Company was awarded a government development contract for a passive detection system known as WINKLE, and a high speed receiving aerial was also installed. Despite the cutting edge technology, in the early days activities at Bushy Hill were restricted to daytime-only working because of complaints that the radars interfered with television reception, as both operated on Band 1 at the time.

This military-industrial site conducting work driven by Cold War concerns would also provide unexpected research legacies for a field far removed from supersonic jets and hydrogen bombs. Clutter caused by the ground had been effectively eliminated by the development of a Moving Target Indicator (MTI), but there were still small echoes appearing, moving slowly and randomly. Due to lack of explanation for these mysterious echoes, they were dubbed “Angels”. There were two possible explanations. During the early years of World War Two, large flocks of birds had been picked up on radar, and even individual large sea birds detected – the Angels could therefore be birds. However, the behaviour of these Angels wasn’t consistent with any known bird behaviour, so it was assumed that they must be pockets of warm air generated by factory chimneys or warm roofs.

Dr Sir Eric Eastwood and a small team had a great many very early mornings at Bushy, recording the flow lines which the Angels followed using a method similar to time-lapse photography. Rings which expanded outwards at dawn, like the ripples on the surface of water when a stone is thrown in, were at first assumed to be caused by the stoking of factory furnace, but an expedition to the site showed that there were not only no factories, and no buildings at all – the location of the rings was in the middle of open countryside! A copse of trees covered with starlings revealed the cause of the strange rings of Angels: successions of waves of birds, separated by three minute intervals, took off from the roost moving in expanding circles to feeding grounds. The Bushy Hill radars also confirmed the suspected “vesper” (evening) flights of swifts, and provided information on the migration of birds.

During subsequent years, Bushy Hill has been used for the development and testing of many systems, as well as being used as a showroom to demonstrate the performance of systems to potential customers. The large radar was also used as a source of radar signals to a number of users, such as the Radar Establishment at Great Malvern, the Marconi Research Centre at Great Baddow, and the RAF at Bawdsey. The RAF used this service to monitor some of its exercises. The site is still operated by BAe Systems as a trials site, so the site itself is not open to visitors, though the surrounding hills are often used for tobogganing.

Thanks to Roy W. Simons, OBE, C. Eng., FIEE, F.I.Mgt., Chris Gardiner of the Marconi Veterans Association, and the MOGS forum for their kind assistance with this article.

*One unexplained effect of clutter was that the Dutch coast appeared to be travelling slowly towards the UK!


Further information

Dr Eric Eastwood, ‘Radar’s Contribution to Studies of Birds’, New Scientist No.282 (1962)

Jack Gough, Watching the Skies: The History of Ground Radar in the Air Defence of the United Kingdom (HMSO, 1993)

R. W. Simons & J. W. Sutherland, ‘Forty Years of Marconi Radar from 1946 to 1986’ GEC Review, Vol. 13, No.3, (1998)


McMillan Sand Filtration Site, Washington, D.C.

Are you looking for something off the tourist track?  What about something that at first sight makes little sense?  Then the McMillan Sand Filtration Site is for you!  Unfortunately, it is closed to visitors but you can the site is bounded by (and you can get good views of it from) North Capitol Street, Channing Street NW, 1st Street NW, and Michigan Avenue NW.  Today, one can glimpse the two paved courts that are lined by regulator houses, tower-like sand bins, sand washers and the gated entrances to the underground filter cells.  Below grade at the twenty-five acre site, there are twenty catacomb-like cells, each an acre in extent, where sand was used to filter water from the Potomac River by way of the Washington Aqueduct.  The treatment was a slow sand filter – a biological treatment system that provided a slow, steady flow of clean water.  For large-scale municipal purposes, the slow sand filter is inefficient and it was replaced in 1985 with a rapid sand filter (which is located across First Street at the McMillan Reservoir.

Diagram of the Washington City Tunnel by the US Army Corps of Engineers.

Before water can be purified, it must get to the McMillan complex and it has always arrived the same way, via the Washington Aqueduct.  The aqueduct was commissioned by Congress in 1852 and construction began in 1853 under the auspices of the US Army Corps of Engineers (who still own and operate the system).  It gradually opened starting on 3 January 1859, was fully open in 1864, and has been in continuous use since.  Water travels through the pipeline from Great Falls to the Dalecarlia Reservoir, and then to the Georgetown Reservoir.  From Georgetown, the water leaves via the “castle” on McArthur Boulevard NW, through an arrow-straight tunnel to the pumping house on 4th Street at the McMillan Reservoir.  The aqueduct is listed as a National Historic Landmark, and the Union Arch Bridge within the system is listed as a Historic Civil Engineering Landmark.

McMillan sand filtration site under construction. Photo by the US Army Corps of Engineers.

The McMillan reservoir, which still holds untreated water for D.C., opened in 1902 and is a dammed stream valley.  The water that flowed through the valley became Tiber Creek and flowed into the Potomac following what is now Constitution Avenue. To clean the water before it was distributed to residents, a filtering plant also had to be constructed as part of the McMillan complex.  At the turn of the 20th century, there was a debate regarding the best practice to purify water – chemical (e.g. chlorine) versus biological (e.g. slow sand).  In D.C., slow sand filtration won out and Congress provided the Army Corp of Engineers with money to build the McMillan Sand Filtration Site.

Photo of Sand Pit being filled with sand. Photo from the US Army Corps of Engineers.

Sand filtration is pretty simple.  Dirty water enters the pit, which contains a two-foot layer of sand, percolates through the sand and is clean when it reaches the bottom, where it is drawn off by a pipe.  While the operation of the filter is simple, the process by which it cleans the water is not.  A slow sand filter works because of the formation of a gelatinous layer called the hypogeal layer or Schmutzdecke in the top few millimetres of the fine sand layer.  It forms in the first couple weeks of operation and consists of bacteria, fungi, protozoa, rotifera, and aquatic insect larvae.  As the Schmutzdecke ages, more algae develops and larger aquatic organisms appear, including bryozoa, snails and Annelid worms.  The Schmutzdecke provides effective purification in potable water treatment, while the underlying sand provides a support medium for this biological treatment layer.  The water produced from a well-managed slow sand filter can be of exceptionally good quality with 90-99% bacterial reduction.  Slow sand filters slowly lose their throughput volume as the Schmutzdecke grows, and it necessary to refurbish the filter to maintain volume (which means removing/disturbing the Schmutzdecke and allowing it to regrow).

The overgrown Clean Sand Silos.

Today, the most visible sign of the site’s history are the overgrown clean sand silos and regulator houses.  The rest of the site is covered in grass, as it was when it was designated the McMillan Reservoir Park in 1906 by Secretary of War William Howard Taft.  It was a memorial to to Senator James McMillan (R-Michigan) for his work as chairman of the Senate Commission on the Improvement of the Park System and his efforts in shaping the development of the city of Washington at turn of the century (aka the McMillan Plan).  After Taft became President, the site was officially designated a park by Congress in 1911.  Originally conceived as part of the “necklace of emeralds” that would ring the city in permanent open green space and restore much of L’Enfant’s original city plans.   In total, the forward-looking plans made by the McMillan Commission called for: re-landscaping the ceremonial core, consisting of the Capitol Grounds and Mall, including new extensions west and south of the Washington Monument; consolidating city railways and alleviating at-grade crossings; clearing slums; designing a coordinated municipal office complex in the triangle formed by Pennsylvanian Avenue, 15th Street, and the Mall, and establishing a comprehensive recreation and park system that would preserve the ring of Civil War fortifications around the city.  The implementation of the McMillan Plan involved the leading civil engineers, urban planners, artists, architects, and designers of the time and at the Reservoir alone, landscape architect Frederick Law Olmsted, Jr., engineer Allen Hazen, sculptor Herbert Adams and architect Charles Platt were involved.  While the engineering work was paid for by the Army Corps, the landscaping work was paid for by the family of Senator McMillan.

Regulator houses such as this one contained valves for controlling the flow of water through each cell.

While it was a functional piece of real estate because of the sand filter, it was topped by “an imaginative combination of landscaped park … personally supervised by Olmsted.”  In a racially segregated D.C., the park was open to all and residents from the ethnically diverse local neighborhoods were delighted to use the park’s amenities.  Courting couples promenaded, families picnicked, and boy played ball games on top of the vaults full of white sand.  Unfortunately, because of security concerns about the safety of Washington’s water supply, the site was closed to the public during World War 2, when a fence was erected around the site; today, it is only open to special visitors and on specially arranged biannual tours.

From its’ completion in 1905 until the Army Corps sold the Sand Filtration Site in 1987, the site was protected from development.  In 1986, the Army Corp declared the land as surplus and the General Services Administration arranged to sale it.  The The District of Columbia government purchased the site in 1987 for $9.3M, in order to facilitate development. Since the time of purchase, the property has been vacant and has deteriorated severely due to lack of maintenance.  Today, the McMillan Park Committee is fighting to maintain it openness and historic character, while the D.C. government is  considering site for dense commercial and residential development. The following video provides an overview of the planning arguments surrounding the site and some great historic images of the area.

Cornish Mines, Cornwall, England

A flash photograph of the Man engine at Dolcoath Mine, Cornwall, 1893

A flash photograph of the Man engine at Dolcoath Mine, Cornwall, 1893. Image available in the Public Domain and licensed via Wikimedia Commons.

Despite being at one far-flung corner of the British Isles, in the eighteenth century the county of Cornwall found itself at the centre (or at least at one centre) of processes that would irrevocably alter British life and Britain’s landscapes: industrialisation. The mining of tin and copper had been undertaken in Cornwall as far back as the Bronze Age, although the practice remained largely unchanged up to the eighteenth century. However, the introduction of the use of gunpowder in the 1690s helped with the sinking of shafts and the driving of levels. Thomas Newcomen’s ‘fire engine’ promised to assist in the problem of flooding in the 1710s but the cost of running the engine proved so prohibitive that by 1740 there were only three of his steam pumps at work in the county.

Improvements were made to the draining of mines using longer and more efficient adits, which were near-horizontal tunnels that allowed water to drain out of the mine by gravity. The situation was improved further in 1777 when James Watt came to Cornwall to supervise the erection of one of his engines at Ting Tang mine in Gwennap, near Redruth. His engines incorporated a separate condenser and easily drained the water that two of the older engines had failed to do and used a quarter of the fuel in the process. This lowered the cost of extracting the copper and helped Cornish miners to compete with cheap Welsh ore. Further advances were made in the construction of these engines by the likes of Jonathan Hornblower and Richard Trevithick. By 1800 Watt’s patent came to an end and with it the burden of royalties and restrictions on innovation. Trevithick built his high-pressure engine and enabled Cornwall’s mines to sink to extraordinary depths and helped the county to become the biggest copper producing region in the world. The demand for tin-plate in the British domestic market in 1800 also fed a tin boom in the nineteenth century, and served as a ready alternative when copper deposits began to run out by mid-century.

Painting of Richard Trevithick, the engineer, by John Linnell (1792-1882), 1816

Painting of Richard Trevithick, the engineer, by John Linnell (1792-1882), 1816. Image available in the Public Domain and licensed via Wikimedia Commons.

The impacts of mining were wide-ranging and felt by all in the county in some way. The population of Cornwall almost doubled, while towns expanded and ports became crowded with ships with orders from around the world. A local manufacturing industry developed in line with the enormous increase in demand for engines and machinery, which led to the establishment of major iron foundries near the mining centres, such as Harvey’s of Hayle and the Perran Foundry at Perranarworthal, near Truro. Transport and communications improved beyond recognition.

The profits that could be made from mining in Cornwall in the eighteenth and nineteenth centuries generated vast new wealth for entrepreneurs and added to that of the old landed families. There were also numerous examples of more modest Cornish families who made their fortune through mining and ancillary industries. While the industrial revolution generated vast wealth for a few, it brought misery to many. With an abundant supply of labour, wages for those employed in mining and industry were pitifully low. Families had to work long hours in almost insufferable conditions when they were malnourished and permanently exposed to disease, polluted environments and hazardous conditions. Unsurprisingly, the gentry lived in constant fear of insurrection as violent protests against living conditions and the price of food were routine. In between the very rich and the very poor, industrialisation helped to create a burgeoning middle class in Cornwall, whose professions were supported, either directly or indirectly, by the influx of capital into the county. It was this eclectic socio-economic group that helped to reshape a Cornish identity rooted in urban industrial prowess, which was added to a longer-held rural identity based on the landed gentry.

Cornwall’s mining and manufacturing industries played a large part in the establishment of scientific societies in the county. The Royal Geological Society of Cornwall, formed in Penzance in 1814, was in fact only the second geological society to be established in Britain, after the Geological Society of London. It was a socially elitist society and many of its leading members were connected to mining, either as landowners or industrialists. The Society opened the first scientific museum in the county, which displayed its impressive collection of minerals, both local and foreign. Cornwall’s second scientific society, the Royal Institution of Cornwall, also invested heavily in the sciences related to mining. It housed Philip Rashleigh’s remarkable collection of minerals, and still does today. The museum is on River Street in Truro. The Institution also developed an educational programme for miners and mining engineers. In 1888 the Camborne School of Mines was established and acted as an important training centre for the region’s miners, although by then Cornwall’s supplies of copper and tin were in decline and many Cornish miners were leaving the county to seek their fortune overseas. The decline and the exodus continued into the twentieth century and was complete by the end of the century. South Crofty was the last Cornish metalliferous mine to close, in March 1998. Cornwall was devastated by the collapse of the industry, both socially and economically. However, its fortunes have improved recently with the Cornwall and West Devon Mining Landscape being granted UNESCO World Heritage status in 2006.


Philip Payton, Cornwall: A History, Fowey, Cornwall Editions, 2004.

John Rowe, Cornwall in the Age of the Industrial Revolution, St Austell, Cornish Hillside Publications, 1993.

William Denny & Brothers Test Tank, Dumbarton, Scotland

Few buildings along the famous River Clyde region of Scotland figure as importantly to the history of shipbuilding, naval science and the British maritime empire than the small and innocuous brick structure that holds the Denny test tank: the world’s first commercial tank (or model basin).

The Denny tank, opened in 1884, was only the second of its kind, built on specifications provided by William Froude, an Oxford-trained mathematician and one-time collaborator with Isambard Kingdom Brunel. Froude designed the first private test tank to provide the British Admiralty with an accurate guide to how full-sized ships would perform at sea.

Well into even the twentieth century, shipbuilders continued to rely on the untrained eye, craft practice and a series of fairly arbitrary calculations to work out the optimum hull shape for ships of all varieties. Froude posited, and then demonstrated, that twelve-foot long model hulls propelled by railway carriage in a water tank 300 meters long would more accurately represent the behaviour of the same said design at sea.

The 300 metre long Denny tank at Dumbarton

The 300 metre long Denny tank at Dumbarton

The British shipbuilding industry was largely unconvinced of the benefits to be derived from Froude’s work, but he did find an influential supporter in the shipbuilder William Denny (whose firm built such ships as the King Edward, the first commercial vessel driven by Charles Parsons steam turbines). In a competitive business community where shipbuilders bid for contracts, accurately estimating ship speed and performance could provide a significant advantage.

William Denny (1847-1887) led his firm through a series of major shipbuilding reforms based on the use of experiments and rigorous sea trials to develop a working knowledge of efficient hull shapes. He instigated the practice of progressive trials to examine the relationship between engine power, speed and hull resistance in different ships; in the mid-1870s he began to closely work with Froude on the analysis of hull resistance; and in 1884 he finished work overseeing the construction of the test tank. He would later write of his firm’s approach to shipbuilding:

A quick and all-round approximation of any new proposal is the only platform from which a professional man can safely start; and it, again, can only be the outcome of years of laborious investigation, and observation, and experiment. The bulk of our brother-ship-builders, and I suspect pretty nearly all your men, don’t yet understand the meaning of this.

Today model testing remains a key part of shipbuilding practice, complimenting computer modelling. The machinery on display at the Dumbarton test tank (now part of the Scottish Maritime Museum) covers a wide chronology, but the museum displays have been presented as ‘Victorian’, complete with mannequin invisible technicians undertaking detailed study of ship curves and test tank measurements – while also moonlighting as night guards to the tank archives stored within the displays.

'Victorian' museum display complete with mannequin invisible technicians

'Victorian' museum display complete with mannequin invisible technicians

Dumbarton is a little over ten miles west of Glasgow. The frequent train service is recommended as it passes alongside the River Clyde, the birthplace of much of Britain’s former maritime empire.

For further details on visiting the tank visit the Scottish Maritime Museum website see http://scottishmaritimemuseum.org/dumbarton.html.

The Clifton Suspension Bridge, Bristol

Clifton Suspension Bridge at night

Clifton Suspension Bridge at night, by Al Howat. Image licensed under Creative Commons Attribution-NoDerivs 2.0 Generic license.

The Clifton Suspension Bridge, spanning the picturesque Avon Gorge, is for many the symbol of the City of Bristol. It is, also, a site for the celebration of not only Victorian science, but also more contemporary innovations.

Its story begins in 1754 with the vision of a Bristol wine merchant who left a legacy to build a bridge over the Gorge. The twenty-four year old Isambard Kingdom Brunel was appointed project engineer – his first major commission. Work began in 1831 but the project was blighted by political and financial difficulties and by 1843, with only the towers completed, the project was abandoned. The Bridge was, however, completed in 1864 at a cost approaching £100,000 in memorial of Brunel who had died five years previously.

Illustration of Clifton Suspension Bridge

Illustration of Clifton Suspension Bridge. Image in Public Domain.

Well, that is one version of the story. Adrian Vaughan, railway historian and biographer of the engineer, claims in his recent book The Intemperate Engineer, that Brunel’s idolatry is not justified – it is shorthand, convenient history. Vaughan argues that Brunel’s reputation today stems from ‘heroic myths’ promoted in a biography from the 1950s by Lionel Thomas Caswell Rolt which glossed over not only the engineers shortcomings, but also the contribution of others. Vaughan’s analysis of Brunel’s diaries and letters at the National Archives, Kew, and at Bristol University, show that the eventual bridge design was fundamentally different from Brunel’s and was the work of William Barlow and Sir John Hawkshaw.

While Brunel’s design had two suspension chains supporting it, the final design had three, with a third more ‘hangers’ – the bard from the chains down to the road. It also had an entirely different system of attaching the ‘hangers’ to the chains, to correct the twisting effect that Brunel’s system would have had on the chains. The method of stiffening under the road was also entirely new. While Brunel had designed a system of wooden struts, these were not considered sufficient so were replaced with riveted, wrought iron, lattice work girders.

We can, however, more readily identify the workings of a more contemporary addition to the Bridge. A question for you: how many light bulbs do you think it takes to illuminate this magnificent structure at night? None. The illumination system – which was switched on at a ceremony in 2006 to mark the 200th birthday of Brunel – is comprised of four elements. Along the length of the chains from which the bridge is suspended are more than 3,000 one watt LEDs (light emitting diodes), in groups of three, each focused on a small section of the chain and throwing into relief the giant nuts which connect the links; Fluorescent tubes beneath the handrail illuminate the walkway and silhouette and emphasize the delicate design of the iron lattice running the length of the bridge; lamps concealed within the arches of the two piers at each end of the bridge, and in the spaces around the top, reinforce the three-dimensional aspects of the bridge. The two sides of each pier are washed with light, carefully directed and focused to avoid the problems associated with urban glow.

Low powered lights concealed beneath each end of the Bridge deck gently downlight the abutments so that, when viewed from the north or south, the Bridge no longer appears to ‘float’ above the Avon Gorge but can be seen to be connected to the structures which support it. The illumination system normally uses no more electricity than a detached house with its domestic appliances switched on.

Palacio de Minería (Palace of Mines), Mexico City

Colegio de Minería (College of Mining) building on Tacuba street in the Centro of Mexico City

Colegio de Minería (College of Mining) building on Tacuba street in the Centro of Mexico City by Thelmadatter. Image available in Public Domain via Wikimedia Commons.

Close to one of the most representative buildings related to arts and culture in Mexico, Palacio de Bellas Artes (Palace of Arts), an architectonic jewel of marble and French style, it is one of the more distinctive places in the history of the National Autonomous University of Mexico (UNAM, in Spanish), Palacio de Minería.

It can be considered a masterpiece of Latin-American neoclassicism, situated at the end of Tacuba Street, and in front on the plaza named Manuel Tolsá (a Valencian sculptor and architect in charge of construction of the Palace), better known as “El Caballito” (“The Little Horse”), because an equestrian statue of Spanish king Charles IV. Palacio de Minería was built to house the Royal Seminar of Mines (also known as the Mining Tribunal) in order to give academic instruction to miners since 1813, after 16 years of construction.

The Palace is usually described like a majestic monument of elegant forms and exact proportions where light, space and functionality merge, and because of this, it is one of the most outstanding constructions in Mexico City, and also it is part of artistic and cultural patrimony of the National Autonomous University of Mexico (UNAM), which, at present time, is under the custody of the School of Engineering.

Inside the Palace, we can find beautiful and marvellous venues like the Ancient Chapel, the Ceremonies’ Hall, the Dean’s Hall, the Principal’s Hall, and the Library, all of them great examples of mural paintings kept as the Manuel Tolsá Museum that houses academies and objects related to his duties as well as masterpieces of some other artists from his time.

In 1954, the School of Engineering moved to the new Campus, Ciudad Universitaria (University City, in the south of the city), which meant a transition era for the Palace: the first year engineering courses were taught in the new Campus, while the traditional careers, such as Mining, Geology and Petroleum Engineering stayed at the Palace, and other areas like Civil, Electromechanical and Topographical Engineering were later studied at University City.

Palacio de Minería

Palacio de Minería by Omar Omar. Image licensed under Creative Commons Attribution-NonCommercial 2.0 license.

The Palace was remodelled and restored in the next years, due a foundation and structural problems that the underground causes in Mexico City, so therefore a refurbishing of the building was carried out by the Former Students’ Society of the School of Engineering. In 1976, after the restoration, the Palace was donated to this school for the use of the school and the students.

Nowadays, this building houses the home office of the Continual and Distance Education Division (DECD), the Engineer Bruno Mascanzoni Information and Documentation Center, the Historical Archives of the Palace of Mines, the Manuel Tolsá Museum, different engineering groups as well as different administrative areas.

Every year the Palace of Mines is used as temporary home office of one of the most important world-wide known publishing events in the country: The International Book Fair.