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From: wsmith@uiucdcsb.CS.UIUC.EDU
Newsgroups: net.physics
Subject: Re: Bogus physics, rotation, Bertrand R
Message-ID: <10800019@uiucdcsb>
Date: Sun, 30-Mar-86 20:00:00 EST
Article-I.D.: uiucdcsb.10800019
Posted: Sun Mar 30 20:00:00 1986
Date-Received: Wed, 2-Apr-86 00:43:32 EST
References: <12706@ucbvax.BERKELEY.EDU>
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Nf-ID: #R:ucbvax.BERKELEY.EDU:12706:uiucdcsb:10800019:000:1896
Nf-From: uiucdcsb.CS.UIUC.EDU!wsmith    Mar 30 19:00:00 1986



>    Let's go back to the Russell quote:
>
>	his predecessors is merely one of convenience; all motion
>	is relative, and there is no difference between the two
>	statements:  `the earth rotates once a day' and `the heavens
>	revolve about the earth once a day.'  The two mean exactly the
>	same thing, just as it means the same thing if I say a certain
>	length is six feet or two yards.  Astronomy is easier if we
>	take the sun as fixed than if we take the earth, just as
>	accounts are easier in decimal coinage.  {Signet, pp. 13-14}

I think there is a more fundamental problem with this statement than the
debate of reference frames.   The statement ignores the difference between a 
tropical day and a sidereal day. 

"the earth rotates once a day"  means that in 24 hours the sun is
	at the (approx) same position in the sky.
"the heavens revolve around the earth once a day" means that after a
	different time period a star returns (approx) to the same position in 
	the sky.

Because there are two rotating motions in the standard reference frame: the 
earth on its axis and the earth around the sun.  The two statements do not
mean "exactly the same thing" there are a different number of days in
a tropical year relative to the sun and sidereal year relative to the
stars.  

I suppose (just to be self-contrary) we could take in the first
quote that he is referring to a sidereal day as well although that is a wierd
interpretation.  If he means by day a typical 24 hour day, than the second
statement is false because the heavens do not rotate around the earth in
a single 24 hour day.
---------
This point is totally irrelevant to the rest of the discussion on the passage
being yelled at or from.  
---------
The terminology in this posting has about a 50% chance of being backwards,
confused or otherwise erroneous, so corrections are welcome.


Bill Smith
ihnp4!uiucdcs!wsmith