Tower Bridge, London, UK, thermogram. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange, red and purple to black (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. This image was captured at night. In the background is the distinctive shape of 30 St Mary Axe, or the 'Gherkin'. Tower Bridge, named due to its proximity to the Tower of London, is a late Victorian lifting bridge. The high level walkways between the towers appear particularly hot. They are now part of a museum about the bridge, although originally they were used by the public crossing the bridge.