Figure 51 is a schematic illustration occupying the full page. It consists of 3 vertical sections. In the left hand section there is a vertical column 6 mm wide and 225 mm high. It is divided into 18 sections. On the left hand side of the column there is a vertical series of 17 numbers labelled “wavelength”. Each number is level with the end of a section in the column. Starting at the bottom and reading up, the wavelengths identified as “1 pm = 10 -12 m, 10 -11 m, 10 -10 m, 1 nm = 10 -9 m, 10 -8 m, 10 -7 m, 1 μm = 10 -6 m, 10 -5 m, 10 -4 m, 1 mm = 10 -3 m, 1 cm = 10 -2 m, 10 -1 m, 1 m = 10 0 m, 10 m, 10 2 m, 1 km = 10 3 m, and finally 10 4 m”. As you read up the column, the wavelength is increasing. On the right hand side of the column there is a vertical series of numbers labelled “frequency”. Each number is level with a tick mark on the side of the column. However, these tick marks are at a point roughly midway through a section on the column. Starting at the bottom and reading up, the frequencies identified as “10 21 Hz, 10 20 Hz, 10 19 Hz, 10 18 Hz, 10 17 Hz, 10 16 Hz, 10 15 Hz, 10 14 Hz, 10 13 Hz, 10 12 Hz = 1 THz, 10 11 Hz, 10 10 Hz, 10 9 Hz = 1 GHz, 10 8 Hz, 10 7 Hz, 10 6 Hz = 1 MHz, 10 5 Hz and finally 10 4 Hz. As you read up the column, the frequencies are reducing. The column is shaded light blue. However, the upper half of the 7 th section up the column is coloured like a rainbow between the labels “10 15 Hz” (on the right) and “1μm = 10 -6 m” (on the left). This completes the description of the left hand section of the illustration. The middle section of the illustration consists of a vertical series of vertical double headed arrows being used to label different sections of the column. These arrows indicate ranges of wavelengths. Starting at the bottom, the first arrow, labelled “γ-rays”, comes from below the illustration (and so it has the lower arrowhead missing) and ends at 10 -11 m. The next arrow, labelled “X-rays”, is between 10 -12 m and 10 -9 m. It overlaps with the γ-rays arrow. The 3 rd arrow, labelled “ultraviolet”, is between 10 -9 m and a bit below 10 -6 m. The 4 th arrow, labelled “visible”, is between a bit below 10 -6 m and just below 10 -6 m. This range corresponds with the upper half of the 7 th section in the column that has the rainbow colouring. The 5 th arrow, labelled “infrared”, is between just below 10 -6 m and 10 -3 m. The 6 th arrow, labelled “microwave”, is between 10 -3 m and 10 -1 m. The 7 th arrow, labelled “radio etc.”, is between 10 -1 m and just above 10 4 m. Along the radio arrow there is another series of labels which reads, starting at the bottom, “UHF (at about 10 -1 m), VHF (at about 1 m), SW (at about 10 m), MW (at about 10 2 m), LW (at about 10 3 m) and VLF (at about 10 4 m)”. They are not quite as evenly distributed as I have implied by the wavelengths. This completes the description of the middle section of the illustration. The right hand section of the illustration has 4 photographs that are being used to exemplify applications for (starting from the bottom) X-rays, infrared, microwave and UHF radio. The X-ray example is an X-ray radiograph of a human foot viewed from above and from the side. The bone structure is visible within the fleshy outline of the foot. The infrared example is an infrared image of what looks like a building. The image comprises areas of different colours that are being used to represent the intensity of radiation being emitted by the building. The darker areas emit lower levels (e.g. roof) and the lighter areas emit higher levels (e.g. the windows). The result is an image that lacks the detail of a photograph but the nature of the object can be recognised (i.e. a building). The microwave example is a picture of the Post Office Tower in London looking up from street level. The microwave radio aerials can be seen around the upper part of the tower. The UHF example is a photograph of an indoor aerial on top of a television set.