# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Interpolation of Meridional Part Table
Date: 2009 Mar 24, 17:00 -0400

```The constant 7915.704468 may be wrong.  That's from Bowditch, 1849.

Sorry about that.  The technique is correct however.

Best Regards

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Brad Morris
Sent: Tuesday, March 24, 2009 4:57 PM
To: NavList@fer3.com
Subject: [NavList 7756] RE: Interpolation of Meridional Part Table

Best Regards

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of NavList@aol.com
Sent: Tuesday, March 24, 2009 3:42 PM
To: NavList@fer3.com
Subject: [NavList 7754] Interpolation of Meridional Part Table

Anyone,
I am looking at a sample problem in section 505 of the 1972 Dutton's.  It says
that the latitude of Cape Flattery Light is 48d23.5' and says that the
meridional parts (m) for that latitude are (is?) 3309.2.

Using an on-line versuion of Bowditch Table 6, I located 48 deg latitude and
went down the minutes column to 23' to find m=3308.8, and to 24' to find
m=3310.3.  A linear interpolation would put 48d23.5' at 1/2 the difference,
or 3309.55 (round up or down to taste), and one would then have m=3309.5 or
3309.6.

I recognize that a linear interpolation doesn't really fit the facts as far as
the way meridional parts change; so is there a technique I shold know about
that would have given me the result Dutton's got, 3309.2?  That is, how did
they do that?

-John Parsons

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