NavList:

   

Reply

Dunthorne makes the simplifying assumption that the effect of parallaxe 
is in the vertical towards the geographical zenith. Strictly, it is the 
geocentric zenith that is at play. Of course, he is not the only one 
amongst his contemporaries to take this practical approach, but in the 
eyes of an astronomie professor editing a manual for the Reichs Marine 
in 1906 this may be a serious flaw. I am only guessing here, because I 
don't have the text of the 1906 edition. The 1854 edition, which is 
online, goes at great length into the corresponding error analysis, but 
it does not mention the 70d to 110d rule. I don't see where it comes from.

Kent posted formulas no. 18 and no. 20. Indeed, no. 20 (which is just a 
prosthaphaeretic transformation of no. 18) is underlying the so called 
"improved Dunthorne" method used in "Tables Requisite..." from the 2nd 
ed. onwards. To understand the criticism we would need to see the 
proposed alternatives, i.e. no. 21 or 23.

Herbert Prinz


Wolfgang K�berer wrote:

>Dear all,
>I think Frank's response to Kent's post may be misleading:
>
>The passage quoted by Kent's colleague is taken out of: "Lehrbuch der
>Navigation. Herausgegeben vom Reichs-Marine-Amt. Zweite umgearbeitete
>Auflage. Zweiter Band. Berlin 1906". And the passage says (in English):
>
>"Regarding the application of these different formulae for deducing the true
>distance the following holds true: Dunthorne's formula (18), or formula 20
>deduced from it, can only be applied, if the distance is between 70d and
>110d. Formulae 21 and 23, on the other hand, can be recommended in all cases
>and are the only ones to be used beyond these limitations."
>
>That - to me - seem to be "reasons mathematical" not "practical". But I
>leave this to the mathematical minds of this group, as I am more of a
>historical bent, as you will remember.
>
>Wolfgang
>  
>




--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply