Nautical mile

[Guest]

Re: Very old fashioned..?

isn't it a chain in length or something silly ..... with so many chains to the furlong and so many f's to the st. mile ????



<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Re: Even more very old fashioned..?

Bugger Napoleon ........ who said it was Napoloeons maths guys ?????


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[tome]

Re: When I was at college ...

This would give a frequency of around 162Hz which is a little slow for matter although it does fall within the range of a French horn!

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[Guest]

Re: Oblate Spheroid I wish

Thank you ....... I remember seeing a NASA phot that showed the earth more sort of pear / come apple shape ...... but as you say oblate spheroid to satsfy the einsteins !!!


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Re: When I was at college ...

I can't remember exactly what they measured the frequency from, but I know that was the basis .... and the measure is a metal bar in Paris under strict climate and quality / sealed environment control ......... if someone please go and have a look at it - I'm sure it will say what the measure is from !!!!


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Left - right ...... Latitude scale on my charts and all charts I used at sea etc. etc. were same both sides of a chart ...... ????????????????????



<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Great and then ....

101 ft ........... its a definition - not a figure !

<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

I apologise for ...

mixing the Mercator projection with the squashed out of shape earth. I should have made myself more clear on that .....

But it still stands : nm = 1 min of arc of latitude


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[tome]

Do you mean the Krypton factor?

In 1790 the French Academy of Science was commissioned by the National Assembly to design a new system of units for use throughout the world. They decided that this system should have the following attributes:

- the system should consist of measuring units based on invariable quantities in nature,
- all units other than the base units should be derived from these base units,
- multiples and sub-multiples of the units should be decimal.

These principles still underpin the modern metric system (SI).

In 1791 the French National Assembly decided in favour of a standard that would be one ten millionth part of a quarter of the earth's circumference. The survey which established the length was made from Dunkirk, in France, to Barcelona, in Spain. The work was long and difficult and was carried out during a time when France and Spain were heading to war. On a number of occasions the surveyors were arrested as spies and nearly lost their heads! From this survey a platinum 'end bar' was produced in 1799 which was known as the 'Mètre des Archives' and was the master standard for the world's new measuring system, the so-called metric system.

Initially this new system was rejected by the French people and it only became rigorously enforced from 1837 onwards: by 1870 it was being widely used in continental Europe.


Between 1892 and 1940 nine determinations of the metre bar in terms of the wavelength of light were made in various laboratories (including two at NPL between 1932 and 1935). The mean of these nine results became the basis of the new definition of the metre as "the length equal to 1 650 763.73 wavelengths in a vacuum of the radiation ... of krypton-86." This was the way that the metre was defined in 1960 and at the same time the International Prototype Metre was replaced.


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[Guest]

6080 ft ......

Stabdardised nm ..... without reference to chart is 6080 feet.

Mercator projection is the world opened out with equator as is, poles stretched out to provide a "square / reactangle" picture. This distorts the world the further north / south you go.

The reason for schools etc. teaching that Latitude is the measurement tool for nm ...... is to stop confusion and possibility of those suing Longitude to measure distance. Can you imagine the error if long scale was used in the upper lats. OK lat is bad enough, but Long is unbelievable. My father was involved in Polar nav with the airlines many years ago and that was mind-boggling .... glad that I wasn't involved !!!! Shell Tankers didn't go to the poles !!!!


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Re: Do you mean the Krypton factor?

Thanks .... I was alos trying to find the text .... I was surfing for it ... but you beat me to it.

So we are BOTH right ........ typical aint it !!!!! And I am not upset that the tone was a bit hard .... its the content that I apreciate and accept. I didn't know about the Napoleon bit and that will be added to lifes lessons ......... we all learn something every day, we never stop learning till we d...

Cheers
Nigel .....



<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Oldhand]

At the Latitude you are at, you ommitted to say.

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[bob_tyler]

Re: Very old fashioned..?

"Old fashioned enough to claim that a cricket pitch is 2 perches long?"

No. Never understood rods, poles or perches but know that a surveyor's chain is/was 22 yards. There is one in a showcase in the NMMC in Falmouth on the Navigation section.

I don't know why its there as I can't imagine it being any use for navigation without two men in diving suits to use it!

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[peterb]

Re: Do you mean the Krypton factor?

You've missed out just one point. The Academy of Science wanted to convert all measurements to a decimal basis, including angular measurement. So instead of degrees they were proposing 100 grads to a rightangle, and 100 mils to a grad, hence 10 000 mils to a rightangle. The kilometre would be the equivalent of the nautical mile, except that instead of using minutes they used mils.

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[LadyInBed]

Re: Do you mean the Krypton factor?

Ah! That explains why they drive on the wrong side of the road /forums/images/icons/shocked.gif

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[craigbalsillie]

Re: another good excuse...

Does that then mean that a cricket pitch in Australia is slightly longer than a cricket pitch in England.(Australia being closer to a pole..)

Maybe that's why the Aussies always beat England at Cricket...

Also a cicket pitch in England will be longer than a pitch in South Africa,
so England should level the series this weekend..

Fantastic news, I bet Nasser wishes he'd taken up sailing , he'd have read this and kept the captaincy..



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[richardandtracy]

Re: Even more very old fashioned..?

Yes, and 20 yards between creases = 4 Rods/ Poles/ Perches (got it wrong earlier - what's going wrong with my maths?!?) at 5 yards long.

Regards

Richard.

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