Knot, Fathom and League

Cecil's Columns/Staff Reports
1

Shouldn’t that be 4830 meters?

2

Freaking tpyos.

3

Cecil didn’t say-- Monty did.

4

Yep, typo… in process of being fixed (or may be fixed by now.) Sorry 'bout that.

5

Can Monty or anyone else give more specifics about the “log line” with the knots in it, and how that worked? Was it somehow attached to a spring so that the faster the boat went, the more the line was pulled out? How was the device calibrated? Were the knots spaced evenly, or was it a “log line” in more ways than one? :wink:

6

It was a knotted rope, knots evenly spaced. When the log was thrown into the water, it stopped dead, relative to the water. So, the speed at which the knots left the boat was your ship’s speed. The corrections due to special relativity were tough, though.

7

This is a page I am working on but the chip log is explained
http://www.geocities.com/alfgon.geo/cninst.htm

8

This thread lead me to the mailbag article it refers to and there is a mistake.

Because of the shape of the earth, a minute of latitude is not the same length everywhere as it diminishes as you go from the equator to the poles.

Length of a degree of latitude:



latitude:  meters:
   90      1848.9
   45      1852.3
    0      1855.4

The nautical mile was defined as 1852 m which is a good average value but NOT the value of a minute of latitude at the equator.

9

The length of a minute of latitude increases as you go from the equator to the poles. That was the result that tipped the scales in favor of Newton’s theory of gravitation.
http://www.svanstein.se/maupertuis/data.htm

This site has some simple diagrams:
http://www.uwgb.edu/dutchs/cosnotes/shapew2.htm

10

RM Mentock, rather than carry on two threads in parallel I will answer in the other thread.

11

That other thread is the one that I linked to earlier
http://boards.straightdope.com/sdmb/showthread.php?threadid=39430