Images Dated 21st November 2003

Egypt. Dahshur. Pyramids

Egypt. Dahshur. Overview of the Red Pyramid, the Bent Pyramid, constructed during the reign of Pharaoh Sneferu (2613-2589 BCE), and the Pyramid of Sesostris III (1878 BC to 1839 BC ) from the Necropolis of Sakkara. Old and Middle Kingdom

© Thaliastock / Mary Evans

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Different coloured Light Emitting Diodes (LEDs)

Blue diode. View of a hand holding the worlds first marketed blue light emitting diode (LED) made from gallium nitride. It is shown with different coloured LEDs. The only blue LEDs available before this were based on silicon carbide. These were very inefficient and did not glow very brightly. LEDs are made of two thin film layers that contain specific impurities which give them opposite electrical properties. An electric current passing through the LED will make it produce light. LEDs were developed in the 1960s but could initially only produce red or green light. In 1995 the Nichia corporation of Japan first marketed these blue LEDs

© VOLKER STEGER/SCIENCE PHOTO LIBRARY

Chemical weights

Assorted chemical weights. The different amount of each chemical represents a measurement known as the mole. One mole of any sample contains the same number of molecules or atoms. The weight (shown in grams) of each molar sample is determined by the weight of the molecules (the molecular weight) and is calculated from the weights of the atoms in the molecule. Three of the chemicals are hydrated with water (H2O). The chemical formulae are, clockwise from lower left: NaCl, FeCl3.6(H2O), CuSO4.5(H2O), KI, Co(NO3)2.6(H2O) and KMnO4. The heaviest atom here is iodine (I), 8 times heavier than oxygen (O). The transition metal compounds are coloured

© ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY