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Alexandre E Eremenko wrote:
>> Somewhere along the line, patent logs
>> (such as the Walker log) were
>> invented and distance was measured
>> directly by trailing the log's
>> spinner.   When?
>>
>
> The first spinning log was apparently invented by
> Edward Massey in 1802, it was in general use by 1836
> and used until 1961. It was improved by
> Alexander Bain in 1946.
> First Walker's log was invented in 1861.
> All these early logs had a disadvantage that the dial
> was close to the screw, so one had to pull the log out
> to see the traveled distance.
>
> Then in 1878 the same Walker invented the "modern" version
> with the dial attached to the taffrail.
> All these logs indicate the distance traveled,
> rather than speed, and one has to use a clock with them.
>
Alexandre:

This last sentence relates to my question.   I suspect patent logs (sucn
as Massey's or Walkers) were used strictly for distance measurement,
since distance traveled is needed for DR navigation, because ships speed
was available via a engine RPM-to-speed table which was very common on
ships a century ago.

You helped answer the most important part of my question -- people
started using direct-reading logs (from which DR could be done) early in
the 19th century.  I guess that the second question might be more
clearly worded "did people switch back to speed measurements before
dropping DR altogether"

Lu

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