Talk:Statmho

What Cardarelli says, and a suggestion for EMU articles

The article currently attributes

1 S ≡ 10⁻⁵c² statmho

1 statmho = 0.00000000000111265005605 S

to

Cardarelli, F. (2003). Encyclopaedia of Scientific Units, Weights and Measures. Their SI Equivalences and Origins. London: Springer. p. 23. ISBN 978-1-4471-1122-1..

Degree of precision aside, it seems strange to write all those zeroes, which then need laborious counting. Why not just say either one-point-something times ten to the minus-something siemens(es), or so many picosiemens(es)?

I don't have a copy of this book. On p.320 of his earlier Scientific Unit Conversion (ISBN 3-540-76022-9), Cardarelli says:

1 statmho = 1, 112650 × 10⁻¹² S

(in which "1, 112..." appears to be a [rare] typo for "1.112..."). I wonder how/why the Wikipedia rendering of what he says in his later book is more confusing than what he says in his earlier one.

In his earlier book, Cardarelli has a brief entry for each of statampere, statcoulomb, statfarad, stathenry, statohm, and statvolt, as well of course as statmho. He also provides a brief explanation of the esu subsystem of cgs on p.17 and a brief explanation of the relationship between esu and emu on pp 17–18. It would be helpful if his book didn't merely identify each of these units as belonging to esu but also pointed the reader to p.17; however, such crossreferencing adds to the bulk of the resulting book and of course is difficult to carry out, so I don't criticize either Cardarelli or Springer for this absence. Since Wikipedia isn't Wiktionary and cross-references are easy to accomplish, I'd be inclined to turn this article and the stub/article on any other esu unit into a redirect to Electrostatic units. -- Hoary (talk) 00:14, 14 January 2015 (UTC) With fairly radical corrections, prompted by Spinning's undeservedly polite comments below. The mistakes were all mine (I blame caffeine deficiency), not Cardarelli's in the slightest. -- Hoary (talk) 01:45, 14 January 2015 (UTC)

PS I've just looked at the history of this article. This version attributes the mindboggling assertion

1 statmho ≡ 0.00000000000111265005605361866087675053350036566001020343907867982125026173889636993408203125 S

to Cardarelli. Does Cardarelli really say that this, or anything like it, is an equivalence? -- Hoary (talk) 00:27, 14 January 2015 (UTC)

As it happens, I went to the library today to look it up for that very issue. Unfortunately, I also had the task of looking up another weights and measures issue in the Fenna source and got the two tasks confused and looked in the wrong sources. So I don't have the Carderelli source (a source some say is unreliable anyway) but do have 1.112650 pS from Fenna (p.76), a much more sensible precision. I really don't believe that Carderelli gives the number cited, I didn't see that sort of precision anywhere in the book. I believe that what the editor has actually done is calculate the ratio 10^5/c^2 using the value c=299792458 (the modern definition of c) although the digits after 618 do not agree with my calculator. This is misguided for a number of reasons, most important is that the value of c in the era these units were used was not 299792458 by definition, but was obtained by measurement, and had a different value. So to take a historic value in statohms and convert it to ohms using the modern value of c will not yield the actual resistance of the historic component. For instance, I happen to know that in Einstein's time (because he quotes the figure) the value of c was taken as 3.01E08. If Einstein were to quote a time interval, say, as 100 km would you recover the original time in seconds by dividing by 299792458? No, you would not, to get the time as measured by Einstein you would have to divide by 301000000.

By the way, this unit is not part of electromagnetic units as you seem to think, but is part of electrostatic units (ESU) for which we supposedly have an article, but it is really no more than a stub. SpinningSpark 01:30, 14 January 2015 (UTC)

Yes, I (and not Cardarelli) idiotically confused ESU and EMU; I've corrected my message above. -- Hoary (talk) 01:45, 14 January 2015 (UTC)

Not generally a helpful thing to alter a post after it has been replied to as it makes a nonsense of the reply, but no worries. My basic point was that the ESU article is a better target if things are going to get merged. SpinningSpark 07:51, 14 January 2015 (UTC)

Abebooks shows copies of Fenna's book (which I haven't seen) for as little as sixty-six pee. Yes, your accountant says you can afford this expense. -- Hoary (talk) 02:22, 14 January 2015 (UTC)

Why are you telling me to go buy Fenna's book. I have already looked in Fenna's book in the library and given the result above. SpinningSpark 07:51, 14 January 2015 (UTC)

I regret that you took it that way. I'd thought I'd point out that copies were extraordinarily cheap, perhaps cheaper than you had realized. Which isn't an entirely negligible matter: the book seems useful for other purposes too, some of the alternatives are quite expensive, and trips to the library aren't always convenient. -- Hoary (talk) 09:09, 14 January 2015 (UTC)

Fine, you buy it if you want to. I have already extracted the relevant information here and have no further need for it. SpinningSpark 14:31, 14 January 2015 (UTC)

I think Hoary was addressing the world at large, here. Sixty-six pee sounds attractive, but then there's the 13 pounds something to my door. FWIW I have the figure 1.1126 x 10^-12 mho, from the McGraw-Hill dict. of sci. and tech. terms, but I have the Japanese translation, which makes it a bit awkward for citing. Imaginatorium (talk) 15:30, 14 January 2015 (UTC)

Yes, I too would have to pay hugely more for postage than for the book itself. ¶ It's perfectly OK to cite a Japanese-language source, even a Japanese edition (very obscure in the anglosphere) of a well-known English-language source. Later, somebody with the good luck to have a copy of the latter within arm's reach can verify that the two books agree and (if they do) convert a citation from the one to a citation from the other. -- Hoary (talk) 00:12, 15 January 2015 (UTC)

I can't tell exactly what Cardarelli wrote, but this all seems a bit odd. The three-line equals means "defined as", no? But a "siemens" was never defined in this way, because it is part of a different system; McGraw-Hill (I bought mine about 1980) uses an inverted Omega, read "mho", I presume. So the "derivation" seems to be backwards... Imaginatorium (talk) 15:52, 14 January 2015 (UTC)

The inverted omega and the name mho are common amongst electrical engineers to mean siemens but this has never been an official part of the SI system of units. I would read ≡ as meaning "identical to" rather than "defined as" in this case. I have seen it used with that meaning in texts before (possibly old fashioned now, I don't know). It is identical by virtue of the ESU system defining vacuum permittivity to be unity. SpinningSpark 16:48, 14 January 2015 (UTC)

But the point is that the "siemens" was only invented around 1970; before that the name for the unit of conductance was ("officially" etc) the mho. It's called the siemens in SI units, but these are not SI units. Anyway, I think the point is that this cries out for someone more knowledgable than I am to write a proper article about the esu system, to replace these stubs. Imaginatorium (talk) 17:08, 14 January 2015 (UTC)