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A couple of months ago, I noted that the etymological story saying that "dead 
reckoning" should really be "ded reckoning" (derived from 'deduced 
reckoning') is more common among flying navigators than floating navigators. 
I've been collecting bits and pieces on this over the past few months, and it 
does still seem to be true that navigators in aviation repeat this 
explanation more often than marine navigators. Also, people who work on 
autonmous navigation/robot navigation also seem to repeat this "etymology." 
Just a difference in culture...

I've tracked down what appears to be the earliest version of this explanation 
of "dead reckoning". I have found no cases before 1920 (and that also could 
explain why aviators picked this up since long-distance air navigation had 
its origins very close to this date). I could not find the original article, 
but this one appears to quote it verbatim:

From "The Rudder" Jan. 1920
"In every ship's log, in all books of instruction, in all works on navigation, 
and in innumerable other publications, we find a special point made of the 
"dead reckoning" on board ship. Why dead? It has been for a century or more a 
stumbling block to investigators, and, as Daniel Defoe would have said, 
"lexicographers have gone astray in this unknown channel." One after another 
has attempted to arrive at some reasonable explanation of it, but has had to 
abandon the task as hopeless, for when they have marshalled all the facts at 
their disposal it is always found that the operations which the word covers 
are anything but dead. They are, indeed, very much alive! 

Henry Harries, acting marine superintendent meteorological office, thus 
explains the phrase in the London Morning Post: "It was not until nearly the 
close of the Eighteenth century that printed log books were supplied by the 
Admiralty. Long before that officers were compelled to keep a journal, the 
form of which was only gradually developed. Originally it was on loose sheets 
of small size, and the columns, when introduced, had to be ruled by hand. The 
log of the Dreadnought, 1679, had twelve very narrow columns on a page. For 
want of space the column for the latitude, 'deduced from the reckoning,' as 
Riddle has it, was headed Ded. Latt. "This abbreviation Ded., for 'deduced,' 
has become corrupted into dead, which has for generations served to exercise 
in vain the most learned savants on two continents to get at its real and in 
the result perfectly simple meaning. There is not a mariner who, on reading 
this explanation, will fail to realize that deduce is the only word which 
correctly expresses the method of obtaining his so-called dead reckoning. He 
deduces his position from the account he has kept, just as any tradesman 
deduces his profit or loss from his account." "

There are a couple of problems with HH's theory. First, the spelling "ded" for 
"dead" was not unusual in the 17th century. English spelling was not yet 
standardized (or is it standardised?). Second, there are early 18th century 
nautical dictionaries that say "dead reckoning" and make no mention at all of 
some earlier spelling or a derivation from "deduced reckoning". That would be 
very hard to account for considering the few decades that had elapsed since 
HH's logbook evidence. Also, he mentions the phrase "deduced from the 
reckoning" which is found in many 19th century navigation manuals. 
Unfortunately for the theory, this phrase was *never* used as a synonym or a 
replacement for dead reckoning. It's not relevant to the origins of the 
phrase. The real etymology is mostly irrelevant today... I can imagine 
something about calculating as if in "dead water" (without currents). But I 
suppose the phrase thrived for generations because it's a bit of comedy: when 
you're "dead", you'll face your "reckoning" (i.e. judgement). Puns have legs.

-FER




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