Dear Marcus, Carl and All, I would like to make a few remarks about the present situation of time measurements in SI.
The SI unit of the quantity, time, is the second, which is defined as: 'The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. This definition refers to a caesium atom in its ground state at a temperature of 0 K.' (The International System of Units, BIPM 1998) As you can see the second is defined, in SI, without reference to any other older way of measuring time. Although this was not always true, the second now stands on its own as a unit of time. Submultiples of the second. For short periods of time we are quite comfortable with milliseconds, microseconds, and more frequently lately, with nanoseconds. All of these are submultiples of the second and they correctly use the SI prefixes for their formation Multiples of the second We have never been comfortable using multiples of the second, except perhaps in space exploration where countdowns can be done in hundreds of seconds. I have never seen anyone regularly use the kilosecond or the megasecond. To put these values into a Babylonian context: 1 kilosecond = 1000 seconds = 1 minute and 40 seconds 1 megasecond = 1 000 000 seconds = 11 days 13 hours 4 minutes and 40 seconds For my calculations you will note that I have used the following definitions from 'The International System of Units', BIPM 1998. Table 6. Non-SI units accepted for use with the International System Name Symbol Value in SI units minute min 1 min = 60 s hour h 1 h = 60 min = 3600 s day d 1 d = 24 h = 86 400 s Notice that the BIPM gives definitions of a minute, an hour, and a day in terms of the only SI unit of time the second and that BIPM does not give any definitions of a week, a month, or a year. Nor does it seem that BIPM regards weeks, months or years as 'Non-SI units accepted for use with the International System'. It is easy to see why this is so there is simply no fixed definition possible for months and years; the length of months varies from 28 days to 31 days (originally for religious and political reasons) and the year is constantly variable over time; the week is defined by only some of the world's religions but not all. Cheers, Pat Naughtin CAMS Geelong, Australia on 2002-07-16 00.44, Ma Be at [EMAIL PROTECTED] wrote: > Dear Carl, first of all, please note that 'convenience' is more of a relative > concept. A good deal of time this characteristic is tied to subjective > opinions; at other times it's driven by applications that use the units in > question. > > These are some of the reasons why we can NEVER satisfy Greeks and Trojans when > it comes to 'convenience'! On the other hand we can *technically* build a > system of units that ARE 'convenient' and by themselves if done properly. And > this is achieved in the SI system. > > The difficulty here though arises when we deal with the *time* construct (the > overwhelming case in your examples). Unfortunately it's fair to say that > while the second is the fundamental unit in SI when it comes to the overall > time framework we do NOT have a cohesive, coherent, consistent construct to > deal with it. What we have is the mediocrity of the stupid Babylonian system > which is evidently non-decimal and does not bode well into the SI construct, > hence 'opinions' like yours (which are very well-founded, mind you. I > unfortunately cannot find strong objections to your post in this regard). > More on this below. > > On Sun, 14 Jul 2002 15:16:53 > Carl Sorenson wrote: >> The point below is an important one. Measuring in seconds is obviously >> superior for many scientific and technical purposes, but in everyday life we >> often use hours. > > If we had a decent agreed-upon time construct our 'hour' would be > decimally-defined and there would be no difference in using the hour or the > second as one would be able to simply move a decimal point to fall into the > other "preferred" unit we may like better! > > Therefore, it's really sad that situations like these as you describe here end > up causing us, metric supporters, a lot of grief, as we unfortunately would > not have something... "better" to offer, at times. I just wished we had 100 > hours in a day though... > >> ... Automobile speedometers give values in km/h because >> those units are more useful when you want to know how long it will take to >> get to your destination. > > Possibly (even though some here may argue that it would be more important for > people to simply be able to... "gauge" how fast someone is going and on that > one, m/s could also do!), but again, if hypothetically we had a 100-hour > framework, for instance, it wouldn't be such a burden to get the m/s value and > "automatically" derive the "equivalent" in 'km/h'!!! Finally... > >> ... It's also more convenient to use degrees Celsius in everyday >> life rather than kelvins. Each of these units can be converted to pure SI >> units without much effort, but they are more convenient. >> ... > The above is a typical case of simply "resetting" where the "zero" is. We do > likewise when it comes to atmospheric pressure, mind you, so, this example is > somewhat... odd in this regard. But, *unitwise* it's technically appropriate > to say that either Celsius or Kelvin provides the same... 'property'. > > Marcus > > > Is your boss reading your email? ....Probably > Keep your messages private by using Lycos Mail. > Sign up today at http://mail.lycos.com >
