![]() Megas also gave us the medical suffix -megaly, meaning “enlargement”- acromegaly, enlargement of the extremities (the hands and feet) hepatomegaly, a swollen liver. There are so many words in micro- and mega- that even I am not tempted to try to list them. The word microscope, for a device to look at small things, had been around since the seventeenth century the less well-known megascope was a nineteenth-century projecting microscope-it threw an enlarged image on to a screen, where it could be traced and turned into a drawing. ![]() And both prefixes had already been doing duty in the scientific vocabulary to designate big things and small things. Mega- comes from megas, “big”, and micro- from micros, “small”. In future, care would be taken to avoid producing more than two prefixes with the same initial letter.īoth mega- and micro- are Greek, which upsets the original system of using Latin for fractions and Greek for multiples. But for micro-, the Greek lower case letter mu (μ) had to be recruited. Mega- was distinguished from milli- by the use of its capital initial (“M”) establishing a precedent for all the multiplier prefixes above kilo. ![]() This created an abbreviation crisis-there were now three prefixes beginning with “m”. The new prefixes were mega-, for a millionfold multiplication, and micro-, for a millionth part of the base unit. The next two prefixes were introduced as part of the definition of the electrical units of measurement, by a committee set up in 1861 by the British Association for the Advancement of Science, under the leadership of Lord Kelvin and James Clerk Maxwell. In the last century we’ve added prefixes only for integer powers of one thousand. There was also a realization that there didn’t need to be a prefix for every power of ten-that would get unwieldy very quickly. Inspired though the original system was, it didn’t offer enough range for scientific use, and the collection of prefixes has been steadily growing. Part 2 dealt with the multipliers- deca-, hecto-, kilo- and myria-, for tenfold, hundredfold, thousandfold and ten-thousandfold multiplication. Part 1 dealt with those original fractional prefixes- deci-, centi- and milli-, designating a tenth, hundredth and thousandth part of the base unit. In my first two posts about the SI unit prefixes, I described how the system originated in the French Republican metric system of 1795.
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