On Wed, 27 Mar 2002 14:38:59 Joseph B. Reid wrote: >Ma Be wrote in USMA 19100: > >> M R wrote: >... >>>According to SI >>>"The second is the duration of 9,192,631,770 periods >>>of radiation corresponding to the transition between 2 >>>hyperfine levels of the ground state of caesium 133 >>>atom. " >>> >>I guess the source of the problem here, Madan, is that you're using a >>deprecated definition of the second. This is no longer how the s has >>being defined. It's now the distance travelled by the speed of light in a >>certain fraction of a second (as much as I believe that this change was a >>huge mistake *conceptually*, we're stuck with it for a while! All >>fundamental units should be defined in terms of *the physical entity it >>tries to define/describe*. In this particular case the use of another >>base unit, the second, for the definition of the meter is totally contrary >>to that principle. But that's the subject for another discussion... :-) >>). > > >On the contrary, Madan is quite right with the latest definition of the >second. Marcus is thinking of the definition of the metre, which is: >"The metre is the length of the path travelled by light in vacuum during a >time interval of 1/299 792 458 of a second.". > Gee! Indeed. What was I thinking? Brain fart, no doubt. Deeply sorry, Madan. On the other hand, my comment concerning the definition of the *metre* stands.
>The advantage of these definitions of the second and the metre is that they >do not depend on the preservation of physical prototyypes. They can be >replicated by any well equipped standardizing laboratory anywhere in the >world. Perhaps so, but what was wrong with the previous one, that didn't need the second for its definition? We're told that this was largely to increase accuracy to 8 decimal places or something to that effect. Now, does this mean we may not have another similar alternative? Just wondering... > The kilogram is the only base unit that now depends on the >preservation of a prototype, "Le Kilogramme prototype" at Le Bureau >International des Poids et Mesures. Note the upper case "K" as a mark of >respect for the prototype. Interesting. Just hoped it would spill over as an acceptable real alternative to lower case "k"... ;-) Marcus See Dave Matthews Band live or win a signed guitar http://r.lycos.com/r/bmgfly_mail_dmb/http://win.ipromotions.com/lycos_020201/splash.asp
