Re: Metric v's Imperial.
Gordon Uber [EMAIL PROTECTED] writes: Let's face it: The Babylonians got it right when they developed the base-60 system. It was applied to the sixth of a circle (one sixtieth of this being a degree) and the hour, of which we still use the first and second minutes. Third minutes (sixtieths of second minutes) are not in common use, although I would note that the third minute of an hour is the period of U.S. power main standard 60 Hz alternating current. Coincidence? Is this the origin of our (English, at least) names for units of time? Seconds because it result from dividing an hour by 60 twice? (Min'-ute, I assume, is related to mi-nute' and mini.) Is it known whether the Babylonians, when they chose 360 degrees to a circle, were more concerned with the convenience of numbers divisible by 2's and 3's or with the fact that there are 360 days in a year (within a percent or two)? --Art
Metric v's Imperial.
Fellow Shadow Watchers, As a teacher within the UK educational system I went entirely metric from the late 60's. If school examinations were to be exclusively metric there was no choice. Everything in Imperial Measure was ruthlessly discarded; not a rod, pole, perch, peck or bushel in sight: and so I remained until retirement. Left to myself I've reverted to 'use whatever is most convenient mode' with feet and inches for 'human scale meaurements' and millimetres for most small things in the workshop. Centimeters were banned from secondary schools and that taboo has stuck. There's a FAX from my metal supplier on my desk this minute quoting for Brass CZ108 1/2 hard 1 off 480mm x 175mm x 5/8 and this 30-ish years after Imperial measurements were supposed to have been discarded. The US of course still use Queen Anne's gallon which the Imperial system replaced with a larger unit later on. We often forget this when comparing fuel prices. The big bit of brass?it's for 'the world's first aggressive gnomon'!! Tony Moss
Re: Metric v's Imperial.
Tony Moss [EMAIL PROTECTED] wrote: The US of course still use Queen Anne's gallon which the Imperial system replaced with a larger unit later on. We often forget this when comparing fuel prices. Tony Moss I guess one could say that Queen Anne's gallon has outlived the imperial gallon which was supposed to replace it... When people get in a huff about how backwards we Americans are for still using inches, pounds, c., I like to reply that the SI still uses the second which is also a ridiculous unit of measure. Quantum units are natural units, but perhaps it's not the most convenient to measure distances in compton radii. The radian is a natural measure of angle, but I would suppose everyone subscribing to this list uses degrees, minutes, and seconds. For example, I haven't seen any of the recent discussion about human visual acuity conducted in terms of radians. Jim 40N45, 111W53 =-= Do not do an immoral thing for moral reasons. -- Thomas Hardy
Re: Metric v's Imperial.
Let's face it: The Babylonians got it right when they developed the base-60 system. It was applied to the sixth of a circle (one sixtieth of this being a degree) and the hour, of which we still use the first and second minutes. Third minutes (sixtieths of second minutes) are not in common use, although I would note that the third minute of an hour is the period of U.S. power main standard 60 Hz alternating current. Coincidence? The arc minute is so convenient for expressing human visual acuity because the value of the latter is coincidentally close to 1 arc minute. For practical calculations at small angles arc minutes and arc seconds are best converted to radians, the arc second being approximately 5 microradians, the arc minute about 17 milliradians. And, of course, the angular diameter of the sun is approximately 10 milliradians. Gordon At 10:55 AM 2/15/00 -0700, Jim_Cobb wrote: The radian is a natural measure of angle, but I would suppose everyone subscribing to this list uses degrees, minutes, and seconds. For example, I haven't seen any of the recent discussion about human visual acuity conducted in terms of radians. Gordon Uber [EMAIL PROTECTED] San Diego, California USA Webmaster: Clocks and Time: http://www.ubr.com/clocks
Re: Metric v's Imperial.
On Tue, 15 Feb 2000, Gordon Uber wrote: Third minutes (sixtieths of second minutes) are not in common use, although I would note that the third minute of an hour is the period of U.S. power main standard 60 Hz alternating current. Coincidence? Hmm... Surprised I never noticed that! Perhaps no more of a coincidence than standard-gauge rail width. The arc minute is so convenient for expressing human visual acuity because the value of the latter is coincidentally close to 1 arc minute. For practical calculations at small angles arc minutes and arc seconds are best converted to radians, the arc second being approximately 5 microradians, the arc minute about 17 milliradians. And, of course, the angular diameter of the sun is approximately 10 milliradians. Gordon Whups! You meant a *degree* is ~17 mRadian, didn't you? An arcsec is very close to 0.3 mR or 300 uR... Still, 0.3 mR for a fine feature, or 1.5 mR for a character are still pretty convenient units for visual acuity. And the Tan function becomes trivial in that regime... Dave
Re: Metric v's Imperial.
And you are quite right, Gordon! I jumped to minutes, from seconds... Something like that usually happens when I nitpick at someone else's typo! How about 5 and 24 uRad for limiting sizes? Dave On Tue, 15 Feb 2000, Gordon Uber wrote: Dave, You are quite correct: 17.45 mrad = 1 deg, not 1 arc minute. However 4.848 microrad = 1 arc second, or approximately 5 microrad. You may be thinking of 1 arc mjnute = 0.2909 mrad Gordon At 02:13 PM 2/15/00 -0800, Dave Bell wrote: Whups! You meant a *degree* is ~17 mRadian, didn't you? An arcsec is very close to 0.3 mR or 300 uR... Still, 0.3 mR for a fine feature, or 1.5 mR for a character are still pretty convenient units for visual acuity. And the Tan function becomes trivial in that regime... Dave
