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Re: Error of Perpendicularity
From: Alexandre Eremenko
Date: 2006 Apr 18, 08:17 -0400
From: Alexandre Eremenko
Date: 2006 Apr 18, 08:17 -0400
Robert, The symbol ^ represents power. So L^2 means L squared (multiplied by itself). Here is the same formula in words: Chauvenet: Error in seconds equals negative 2 times sin1" times (error in perpendiculatiry, squared) times tangent of one quarter of the angle. Hope this helps. I bought Chauvenet in some web book store for much less than $300. I don't think I payed more than $50 for the set of two volumes in excellent condition. (I don't remember what the exact price was, but I would definitely not buy it for more than $50, because my university library has it, and the library is next to my office. So yesterday I used the library copy to reply your message quickly:-) Alex On Mon, 17 Apr 2006, Robert Eno wrote: > > Thanks Alexander > > Quick question: > > Does the ^ symbol represent multiplication? > > I am having a bit of trouble following the sequence of calculations in the > formula. > > Any chance of your scanning in that particular page and sending to me? > > I've always wanted a copy of Chauvenet but the $300 plus price tag deters > me. > > cheers, > > Robert > ----- Original Message ----- > From: "Alexandre E Eremenko"> To: > Sent: Monday, April 17, 2006 2:21 PM > Subject: Re: Error of Perpendicularity > > > > Dear Robert, > > The only book I know that contains a COMPLETE > > theory of sextant is Chauvenet. (I am sure that there > > are others, but this is really complete, very concise, > > and written in good English:-) > > > > In particular, on p. 115 (vol. 2) the following formula > > is derived: > > Err=-2 L^2 sin1" tan(h/4), > > where Err is the resulting error, in seconds > > L is the deviation of your mirror from > > perpendicularity (in seconds) and h the angle you measure. > > > > In more modern notation this becomes: > > Err=-0.00057 L^2 tan(h/4) > > where both Err and L are in minutes now. > > > > For example, if L=5' > > Then Err=0.008 or 05", which is completely negligible. > > > > Now, according to SNO manual, you can adjust this mirror > > (using special factory-supplied visors in place of dominoes) > > > > That's why visual adjustment (without dominoes) is OK too. > > Two years ago there was a large discussion on the list about > > how exactly to do this adjustment, and the general conclusion > > was that dominoes (or visors) are only recommended for sextants > > with front-silvered index mirros. > > For back silvered mirrors, the usual eye method is OK. > > > > Alex > > >