# When Units Collide **URL:** \ **Category:** Factual Questions\ **Created:** [May 16, 2006, 11:03pm UTC](https://boards.straightdope.com/t/when-units-collide/357038 "2006-05-16T23:03:34Z")\ **Posts on this page:** 13\ **Page:** 3
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 18, 2006, 9:14pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/41 "2006-05-18T21:14:25Z")
> [@Chronos](#): > > Quoth **Colibri** :Could you elaborate a bit on this? The definition as you state it here seems to be both circular and inconsistent. The 2.718 suggests to me that there’s something exponential going on, but I’m not sure how that would manifest. The darwin is not used very much, especially now. An outline is [here](http://www.colorado.edu/epob/epob3250mgrant/public_html/12thwk.html) > [@](#): > > Darwin–a unit of evolutionary change defined as 2.718 units of change/million years > 1. the units vary depending upon what trait is being studied; might be cm for length, square cm for areas, etc. > 2. Calculational formula: r = (lnX2 - ln X1)/millions of years where r is the rate of evolutionary change in Darwins, ln is the natural logarithm, X2 is the measure of the trait at time two (later) and X1 is the measure of the trait at the earliest time. > 3. Example: Some trait was 13 cm at a point in the geological record 3 million years later than the first sample. The first sample was measured at 10 cm. The rate of change for that trait, in Darwins, r = ((ln(13)-ln(10))/3 = 0.0874 It’s basically just a way to compare rates of morphological change in different lineages. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [May 18, 2006, 11:20pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/42 "2006-05-18T23:20:01Z")
> [@Askance](#): > > it’s interesting how there was a golden period of unit-naming in the mid-19th century and consequently many of the much smaller pool of individuals involved in science at the time did meet. To put things in a little context, there is a non-accidental pattern to the associations in the 19th century and the subsequent naming of units. Questions about universal standards and units for electricity and magnetism were a big issue in physics in the second half of the century. To a certain extent the concepts couldn’t even be systematised until then, but there was also practical pressures from the newly created telegraph industry to establish reliable standards. Kelvin, Weber and Siemens were all central players in the debate about how this should be done, with both Joule and, somewhat later, Hertz also making significant contributions to these arguments. This is a group who, even if they never actually met, were aware of each other, read each others papers and usually corresponded, even as they often took up different positions in that debate. Out of their arguments emerged the definitions and names for the likes of the amp, volt and ohm. It’s thus hardly surprising that when it came to define the units for thermodynamics and the later electromagnetic ones, these were the sorts of names that were proposed. People have that tendency to honour those whose footsteps they see themselves following in. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [May 18, 2006, 11:53pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/43 "2006-05-18T23:53:27Z")
And let us not forget the Middle eastern Ernest L. Cubit and his much later English descendent, Bernard Foote. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 19, 2006, 6:05am UTC](https://boards.straightdope.com/t/when-units-collide/357038/44 "2006-05-19T06:05:58Z")
OK, that makes more sense. The way you phrased it before, it came off as “One unit is equal to 2.718 units”, which doesn’t make much sense, but it seems that it should be better described as “change in a numerical trait by a factor of _e_ per million years”, which is much more reasonable. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 19, 2006, 6:11am UTC](https://boards.straightdope.com/t/when-units-collide/357038/45 "2006-05-19T06:11:33Z")
> [@Sunspace](#): > > It’s a unit of electrical inductance, a measurement of the energy that can be stored in the expanding magnetic field around a coil through which a changing current is passing. I think. Close enough. Specifically, the Henry is defined as the amount of inductance in which a current change of one ampere per second will induce a back EMF of one volt. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [May 19, 2006, 8:13am UTC](https://boards.straightdope.com/t/when-units-collide/357038/46 "2006-05-19T08:13:51Z")
> [@tschild](#): > > The English phrase might be a partial translation of the German phrase _aus dem Schneider_ (literally, out of the/off the tailor). The general meaning of the phrase is being “off the hook” for something (i.e. not having to fear adverse consequences) or having achieved enough, and the specific meaning in the [Skat](http://en.wikipedia.org/wiki/Skat) card game is scoring more than 30 points. > > _Schneider_ in German literally means cutter but in fact means tailor. A mere cloth cutter would be a _Zuschneider_. > > The explanations that I read for the _aus dem Schneider_ phrase were essentially that tailors were reputed to be slight, unmuscular, even crippled people (who were too weak for more energetic work), and that _Schneider_ was used to refer, by extension, to a slight person and, by extension from that, to a small quantity. _Nine and twenty tailors went to catch a snail; The bravest man among them durst not touch her tail! She put out her horns like a little Kyloe cow - Run, tailors, run, or she’ll kill you all e’en now!_. ---
**Author:** ![GargoyleWB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gargoylewb/32/199_2.png) [@GargoyleWB](https://boards.straightdope.com/u/GargoyleWB)\ **Post date:** [May 19, 2006, 4:41pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/47 "2006-05-19T16:41:15Z")
There is the [Batman](http://en.wikipedia.org/wiki/Batman_%28mass_measure%29) , a unit of weight. Although now obsolete, I suggest that we now use it as a standard way to measure preparedness. ---
**Author:** ![GargoyleWB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gargoylewb/32/199_2.png) [@GargoyleWB](https://boards.straightdope.com/u/GargoyleWB)\ **Post date:** [May 19, 2006, 4:54pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/48 "2006-05-19T16:54:57Z")
A few more folks to add to the Six Degrees of Kelvin game… Wilhelm Rontgen (1845-1923) (rontgen radiation unit) Samuel Langley (1834-1906) (langley unit of solar radiation) Max Planck (1858-1947) (planck mass, planck weight, planck scale, etc) Anders Angstrom (1814-1874) (angstrom unit of length) ---
**Author:** ![GargoyleWB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gargoylewb/32/199_2.png) [@GargoyleWB](https://boards.straightdope.com/u/GargoyleWB)\ **Post date:** [May 19, 2006, 6:07pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/49 "2006-05-19T18:07:33Z")
Forgive the trickle-posting. I remembered one that doesn’t seem to be mentioned, yet I use it on the job nearly everyday. :smack: Curiously, the unit also seems to be absent from Wikipedia. Johann Lambert (1728-1777) (the lambert = lumen / cm^2) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 19, 2006, 7:09pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/50 "2006-05-19T19:09:02Z")
> [@TJdude825](#): > > Bonus Question 2: You already know that the unit of capacitance, the farad, is named for Faraday. But what _other_ unit is named for him? The Faraday, a unit of electrical charge. It is equal to about 94.49 kilocoulombs and is defined as the charge carried by one mole of electrons. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [May 20, 2006, 12:44pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/51 "2006-05-20T12:44:55Z")
To try to keep things managable, I’ve been inclined to ignore the names mentioned where they’re not the main, widely used SI cases. (There are all sorts of units that could be mentioned. Just in the last couple of months, the Bethe was suggested as a unit for supernova energy. Will this catch on? Unlikely.) But Darwin and Planck are worth a mention. For the most interesting example of an important 19th century scientist who Kelvin _didn’t_ meet is Darwin, despite his prominent role in the post-1859 debate about the geological timescale. However, Darwin’s son George, who became a distinguished physicist in very much the Thomsonian manner, did know him well and collaborated with him. As for Darwin and Faraday, they also don’t appear to have met, even though the latter was good friends with the likes of Gideon Mantell and Lyell and so was familiar with Darwin’s professional circles. However, there is some evidence that Darwin got John Murray, as his publisher, to send a presentation copy of the first edition of the _Origin_ to Faraday. But that was presumably just because of his status by this stage as the grand old man of British science. Since his mind, and specifically his concentration, was going by then, I doubt Faraday ever read the book. In fact, I don’t think that Darwin met _any_ of the names mentioned above. Planck probably didn’t meet Kelvin either, though given that his research was mainly in thermodynamics it’s difficult to believe that he wouldn’t have accepted a chance to meet had one arisen. I suspect he probably knew Hertz, who left Kiel in the same year - 1885 - that he was appointed to the same department and it was a town to which he had prior family connections. Like Hertz, he had professional run-ins with Weber, but I don’t know if they actually met. The encounter between Planck and one of the names mentioned above that is extremely notable is with Einstein, since it was him who was the established figure in physics who read the first paper on special relativity and, more or less immediately, realised its significance. His follow-up letter he wrote to Bern was the first step in Einstein’s rise to international recognition. They didn’t actually meet until a couple of years later, but they became good friends and later saw a lot of each other in Berlin. Since it hasn’t been mentioned yet, Gauss and Weber were close colleagues. The [monument to them in Göttingen](http://www.utsc.utoronto.ca/~lzhao/Gallery/Goettingen/goettingen.html) specifically commorates their partnership. But, per the OP, this is a case where it was their joint work on geomagnetism that was partially - though not exclusively - being marked by naming the units after them. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [May 20, 2006, 4:22pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/52 "2006-05-20T16:22:56Z")
> [@GargoyleWB](#): > > There is the [Batman](http://en.wikipedia.org/wiki/Batman_%28mass_measure%29) , a unit of weight. > > Although now obsolete, I suggest that we now use it as a standard way to measure preparedness. And like the farad and the henry, it’s an inconveniently large unit, and most of use could get by with milliBatmans or even microBatmans. ---
**Author:** ![JR\_Brown](https://avatars.discourse-cdn.com/v4/letter/j/d6d6ee/32.png) [@JR\_Brown](https://boards.straightdope.com/u/JR_Brown)\ **Post date:** [May 22, 2006, 8:25pm UTC](https://boards.straightdope.com/t/when-units-collide/357038/53 "2006-05-22T20:25:46Z")
> [@UncleBeer](#): > > The _lumen_ is named for Louis Jean Lumière. > The _phot_ for Photius I of Constantinople. > [snip] > The atomic mass unit _amu_ is sometimes called the _Dalton_ after the chemist John Dalton. > [@TJdude825](#): > > I always assumed the lumen was from the Greek or Latin or something for “light” but then I suppose that would be “luc-” not “lum-”… interesting. Hmmm… It seems to me unlikely that the phot was named after a 9th century bishop who had no apparent scientific bent (he did do a lot of literary writing). Much more likely that it derives from the Greek for “light” (phos; phot- as a prefix). Likewise, I’ll bet cash money that the lumen is derived from the Latin word “lumen” (light) and not the French filmmakers. _The Oxford Dictionary of English_ agrees with me on both of these. The Dalton is alive and well in biology; the sizes of proteins are generally given in kiloDaltons, not amu’s. JRB [Previous page](https://boards.straightdope.com/t/when-units-collide/357038.md?page=2)