If you want to understand a log, the place to begin is with the nautical mile, which is exactly 1000 fathoms, 6000 feet, or the distance covered by one minute of latitude. Once you understand that simple relationship, most of the rest of the calculations to do with navigation become easy indeed.
This wasted logs, and was unreliable, so before long, the log was dropped with a line attached to it, to see how much of the line paid out in 30 seconds or 60 seconds, measured by a sand-glass.
The old dropped log was not entirely forgotten, because English sailors called this a Dutchman's log, but they soon found a better design to use.
|Jeffery Walker's patent log rotator|
Then somebody had a clever idea: put knots in the line, and count them as they go through your hand. If these knots are 1/120 of a nautical mile (50 feet) apart, then each knot paid out in 30 seconds indicates one nautical mile an hour, while knots at 100 foot intervals are used for a sandglass period of 60 seconds.
Later, better ways were found of getting the measurement, like Walker's patent log rotator, shown on the left,
No matter how they were obtained, the results were, of course, written in a 'log book', and that term came to apply to any record, such as the record of people accessing a computer system.
And that is why, today, we 'log on' to a computer system, though few of us spare much thought, as we do, of the horny-handed old salts who heaved lumps of wood over the side of old sailing ships.
Bloggers think about their origins even less.