 and equivalent to one tenth of a nanometre. This means that a nanometre is equivalent to 10 hydrogen atoms sitting shoulder to shoulder (assuming this is what hydrogen atoms like doing). This is remarkable given that in 1850, the metre was an ill-defined measure and dangerously French. In the 1790s when Fourier was thinking about his transforms during the French revolution, his compatriots were deciding that the metre should be made equivalent to one ten millionth of the length of the meridian running through Paris from the pole to the equator on the basis that Paris was and still is the centre of the world if not the universe in general. Unfortunately, this distance was miscalculated (a failure to account for the flattening of the world by rotation) and SO the metre was set to an arbitrary length referenced to a bar of rather dull platinum-iridium alloy. This was redefined in 1889 using an equally arbitrary and equally dull length of platinum-iridium, then redefined again in 1960 with a definition based on a wavelength of krypton-86 radiation (the stuff that Superman uses SO at least slightly less dull). In 1983 the metre was redefined as the length of the path travelled by light in a vacuum during a time interval of /1/299 792 458 of a second, which effectively determined the speed of light as 299 792 458 metres per second. This is not the same basis upon which radio waves are measured and not the same way that Angstroms are measured. Anders Jonas Angstrom's work (1814-1874) was carried on by his son Knut (1857-1910) and formed a body of work that remains directly relevant today to the science of optical measurement. The Optical Pipe and Pixels 10.3.1 Pixels and People We have said that the sensor array emulates the functionality of the human visual system in that it takes point measurements of light intensity at three wavelengths (red, green and blue). A 4-megapixel sensor will have four million pixels most of which will be capturing photons and turning them into an electron count that can be used to describe