Author: Andrew Grantham

Conservation of the concrete mirrors

Posted on by Andrew Grantham

When I went on one of the guided walks to the Denge sound mirrors, one of the other vistors was a construction worker who was somewhat critical of the quality of some of the original concrete on the mirrors. I’m not qualified to comment, but Rowan Technologies has some experts on the conservation of concrete.

Case Study #1: Dungeness

English Heritage has commissioned a series of investigative repairs on the mirrors – which are now scheduled as monuments (legal protection specifically for archaeological sites) – that will explore treatments that might be transferable elsewhere. The richly patinated surface of the mirrors is a complex amalgam of weathered aggregate and many varieties of lichen. Chris Wood from English Heritage’s building conservation team is also experimenting with yoghurt to encourage lichen reinstatement. The works were carried out by Rowan Technologies.
Source: The Architects’ Journal, 2008-11-24

Rowan Technologies has this to say:

Conservation Case Studies

The Listening Mirrors, Kent
Like-for-Like Concrete Repairs

The three early warning sound mirrors [at Denge] on the Kent coast were built using reinforced concrete in the late 1920s and the early 1930s to detect the distant sounds of enemy aircraft approaching from over the English Channel. The reinforced concrete has deteriorated in the marine environment and many parts of the structure are suffering from corrosion of the reinforcements and the delamination of the concrete cover.

Rowan Technologies undertook a series of trials of various repair and rehabilitation methods to assess their suitability for these monuments. This included ‘model’ patch repairs of the damaged concrete on a like-for-like basis, to achieving a similar texture and surface finish to the original
Source: Rowan Technologies Ltd

‘Hidden things to see and do’ from the Observer

Posted on by Andrew Grantham

The sound mirrors – and this website – got a mention in the Observer’s travel section on 5 April 2009. The piece formed part of the Military sites” category in a series about Secret Britain – “All around us lie overgrown and forgotten sites with fascinating stories to tell, says Iain Sinclair”.

Acoustic mirrors, various locations

In the middle of a field in Kilnsea, Yorkshire there is a 15-foot-high concave concrete structure resembling a satellite dish. It’s actually an acoustic (or sound) mirror, used during the first world war to detect enemy engine sounds. They are a common fixture along the British coast, including at Kilnsea (OS map ref: TA 411167), Hythe in Kent (OS map ref: TR138344) and Denge on the Dungeness peninsula (OS map ref: TR070215), which recently featured in the new Prodigy music video, Invaders Must Die.
Source Observer

The Devil of Denge Marsh

Posted on by Andrew Grantham

I think it must have been a radio programme, or something like that… the picture seems to show an aloe vera plant attacking the 30 foot mirror at Denge.

The Scarifyers return in their second full-length adventure…

A melting minister… a scientific project gripped by madness…
a remote village on the Kent coast where the locals have some strange habits indeed. It’s all just the ticket for top-secret government department, MI-13.

Lionheart (Nicholas Courtney) and Dunning (Terry Molloy) are back, to do battle with the Women’s Institute, an old adversary and an inter-dimensional being from the dawn of time – THE DEVIL OF DENGE MARSH.
Source: Cosmic Hobo

Denge sound mirrors feature in prize-winning graphic story

Posted on by Andrew Grantham

Julian Hanshaw won the 2008 Observer/Cape Graphic Short Story Prize with Sand Dunes and Sonic Booms, described by the Observer as a “haunting, evocative and beautifully drawn story”. It is set on the south coast, and at the Denge mirrors in particular.

We loved Hanshaw’s sense of time and place – an effect he achieved partly through a series of sepia frames illustrating the south coast. Hanshaw is an animator by training, and moved to Winchelsea, East Sussex from London three years ago. Since then he has become ‘mildly obsessed’ with the area, particularly the spectral and strange Dungeness. The idea for ‘Sand Dunes and Sonic Booms’ came after a visit to one of the south coast’s sound mirrors – primitive devices designed to detect and track military aircraft before the First World War (though the ones in Kent date from the 1930s).
Source: The Observer 2009-11-09

You can read the story here: Sand Dunes & Sonic Booms.

Parabolic sound mirrors to reflect and focus sound

Posted on by Andrew Grantham

The Whipple Museum of the History of Science in Cambridge has a webpage about some parabolic sound mirrors to reflect and focus sound.

This apparatus consists of a pair of brass parabolic reflectors mounted on wooden stands. One of the reflectors has a bracket with a hook for hanging a pocket watch. The demonstrator would use this apparatus to show how the sound of a ticking watch may be heard at a considerable distance having first been made into a beam, projected over a distance and refocused. Very little is known about this pair of mirrors in the Whipple’s collection. It is thought that they were made in France or Germany during the second quarter of the nineteenth century.
Source: Whipple Museum of the History of Science