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The following was taken from an Cox, Hargreaves and Thomson, Limited publication entitled Optos. It featured
several paragraphs and drawings of the tunnels which are reproduced below. Only the sections featuring the tunnels are included.
The Workshops"Apart from the 'know-how', our workshops are our primary asset. They consist of long, intersecting, underground tunnels which were built during the war for air-raid shelters. They are some 50 feet below the surface. We can therefore rely on constant temperature the whole year round and enjoy the benefits of still air and freedom from vibration. These are of course very great assets in this class of optical work. Such ideal conditions make it possible for us to detect and correct errors that would otherwise remain unnoticed and we are thus able to do just that extra amount of work which makes the difference between a "good enough" optical surface and a perfect one."
Cox, Hargreaves and Thomson, Limited, Underground Optical Works"The tunnels are brick lined, with vaulted roofs, and are 9 feet high and 7 feet wide. The chamber at the North end of the first transverse tunnel is 30 feet long, 10 feet wide and 10 feet high. The large polishing machine, capable of dealing with mirrors up to 80 inches diameter, is situated in this chamber, and the whole length of the transverse tunnel (235 feet) is available for testing. The length available in the central longitudinal tunnel is 240 feet.The original contour of the ground is indicated by the dotted line in the sectional view."
"At the far end of the central tunnel a ventilating shaft extends to the surface. An air-conditioning apparatus at X draws air down the shaft and extracts some of the moisture, but does not change its temperature. The air issuing from the lower end of the ventilating shaft is always saturated and at a tempearture of 54oF, whatever the external temperature and humidity may be."
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