Wikipedia:Reference desk/Archives/Science/2018 July 3

= July 3 =

Outstretched Fingers Form Circular Pattern
When outstretched, the fingers of the human hand seem to form a circular pattern. Is it true ? Is it known ? If so, what would be the biological explanation ? — 79.118.184.15 (talk) 03:45, 3 July 2018 (UTC)
 * I'm not seeing anything obvious in Google, but here's something you could try: Position your hand in that way on a piece of paper, and put a mark for each fingertip. Then see if you can fit a circle to it. ←Baseball Bugs What's up, Doc? carrots→ 04:36, 3 July 2018 (UTC)
 * The center of the circle seems to coincide with the center of the palm. Furthermore, the lengths of the pinky and the thumb appear equal, as do those of the index and ring finger. — 81.196.204.42 (talk) 16:41, 3 July 2018 (UTC)
 * The biological explanation is that the fingers radiate from the carpals, as shown in this animation.--Shantavira|feed me 06:23, 3 July 2018 (UTC)
 * It looks oval rather than circular. ←Baseball Bugs What's up, Doc? carrots→ 12:00, 3 July 2018 (UTC)

The subject at hand (!) could have been a better wing, flipper or purr-fect scratchy-grippy tool but instead you have something that does better than any of them on any of these. DroneB (talk) 14:03, 3 July 2018 (UTC)
 * I'm not quite sure what the OP is referring to, but digit ratio seems to be the appropriate article; there are apparently lots of things that influence finger length ratios (and hence the overall shape of the outstretched hand). Matt Deres (talk) 15:29, 3 July 2018 (UTC)


 * The immediate developmental reason is that the limb bud forms a rough circle, which is carved up by apoptosis into individual fingers. Of course, this doesn't have to lead on to a final circular pattern -- see File:Pterosaur Wing Anatomy.png about pterosaurs.  It is not straightforward to decide whether fingers are the same length because this development is just "easier" or whether there is an adaptive reason (easier to clutch a fistful of silver ... probably not) Wnt (talk) 10:24, 4 July 2018 (UTC)

Diesel engines
I was asked to put this in a separate question. If a diesel engine burns pure cetane it's probably a standardized cetane number testing engine burning it for a short time maybe for calibration or something and that for the purposes of comparability might have its design frozen since the invention of cetane numbers and thus not have to deal with the many thousands of injector psis or hundreds of thousands of miles of modern engines. So I'm wondering if 100% n-hexadecane is just overkill or if it'd actually be a poor fuel for other reasons like lubricity even in like Nauru (all time low temperature: 20C, melting point: 18) Sagittarian Milky Way (talk) 19:52, 3 July 2018 (UTC)