The letters in the highlighted squares are G, O, R, E, N, E, C, A, T, M, F, R and I. Rearranged, these spell FERROMAGNETIC. Some common examples of ferromagnetic materials are iron (Fe, 32 Across), cobalt (Co, 21 Across) and erbium-nickel (Er, 23 Across) alloy.
You have probably carried out experiments in school on the refraction of a light ray when it passes between air and an optically more dense medium, such as glass or Perspex, and will remember that the angles of incidence and refraction are measured against an imaginary line perpendicular to the media boundary called the normal (8 Across). The term normal originates from the Latin for ‘carpenter’s square’ and is taken to mean ‘perpendicular to’. Light refracts because it changes velocity as it crosses the boundary between media.
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