Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: Lecky's mistake
    From: David C
    Date: 2020 Oct 31, 13:53 -0700

    Frank I take your point about knots through the hand.

    David I have a pdf of the 1884 Lecky open at the pages you have posted (must buy a hard copyy). Lecky refers to William Thomson, the 1st Baron kelvin. Clearly Kelvin had a big influence on Lecky. The reason I have Lecky open is that I am trying to understand Alfred Chalice Johnson's (aka Cloudy weather Johnson) double chronometer method. Johnson clearly understood the concept of and advantages of position lines. He understood that position could be determined by taking two time sights and crossing the Sumner lines. There was a downside to the Sumner methor - the amount of computation and the mess created on charts by plotting. In about 1880 Johnson published "On Finding the Latitude and Longitude in Cloudy Weather" in which he introduced the C tables (A+B=C). He described a method for calculating position from two time sights, the ABC tables (johnson's table I and table II) and plane trigonometry.

    We can conclude that by the 1880s navigators such as Lecky and Johnson undertood position line navigation although the morning/noon sight method probably remained in use with most navigators well into the 20th century.

    I have successfully calculated my latitude by Johnson's method but have not been successful with longitude. I am hoping to sort that out today and maybe will post details of how Johnson's the method works. The 1905 copy of Johnson was the 28th edition - roughly  a new edition each year, suggesting that his method was very popular.

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site