I picked up a book of words in a book store today and found some interesting
metric refernces in it. The book was a dictionary-like compilation, with
definitions, of words that are often incorrectly used, incorrectly spelled
or incorrectly pronounced. I don't know what the author's criteria were for
deciding to include or exclude a word in the book.
Leafing through it, I spotted a word or two that started with "milli" so I
stopped and read more carefully. There were of course a couple words that
had nothing to do with the metric prefix, but I was amazed that they used a
lot of space (most of two pages) to list a lot of SI units with the milli
prefix attached.
Surely they could have simply listed the prefix "milli-" and indicated that
it can be used with any SI unit (and is often used with non-SI units as
well). I believe the various basic SI units were in the book as well. I
should have checked but didn't. (I wonder if they used the term "SI" to
describe them.)
Among the milli words the book contained that were prefixed SI units, I
recall seeing a lot of less than common ones like milliampere, millilux,
millifarad, millimole, millicoulomb, millihenry etc. Interestingly, in spite
of a rather complete set of electrical units, I did not find millivolt,
which is relatively common.
In all cases where the word was a legitimate SI prefixed unit the book gave
the correct SI symbol (even to the use of omega in milliohms, m�). But they
called the symbols "abbreviations" and often gave secondary "abbreviations"
as well, never correct SI.
I also saw milliere (I think I recall the spelling correctly) which was
identified as 1000 kilograms! Of course, we call it a megagram or a metric
tonne. I never heard of that one. Has anyone else seen the word "milliere"
used?
I also saw the milliangstrom, identified as a unit for measuring the
wavelength of light. I never heard of that unit being used in that way.
Since light has wavelengths approximely from 4000 angstroms to 7000
angstroms (400 nm to 700 nm) it was usually (in the past) measured in
angstroms (and is now measured in nanometres, nm). There are no wavelengths
of light that would be small enough to measure in milliangstroms. Of course,
one could refer
to 4000 angstroms as 4 000 000 milliangstroms but what would be the point of
doing so?
(From the non-technical tone of the rest of this book, I am assuming that by
"light" the author meant "visible light". If they had meant anything
broader, especially if they meant something down in the milliangstom range,
they would certainly have called it "electromagnetic radiation" or
something, not "light".)
One of the other non-SI references was to the millimicron, an older and now
deprecated name for the nanometre. Interestingly, they gave the symbol for
millimicron as "m�" ("em mu", both lower case). Thinking back on it, I wish
I had checked the listings under "micro" to see if they had given the SI
units of a variety of real SI units with the micro prefix and if they used
the correct symbol, the Greek mu. Since they used mu in the symbol for the
non-SI unit millimicron, I'm guessing they used it for the micro prefix on
SI symbols, also.
It was interesting to see the inclusion of so many units of the SI system in
this non-technical book.
Regards, Bill Hooper
retired physics professor, Florida, USA
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"Simplification" begins with "SI"
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