Woke up this morning to think about calibrating the new compass, having vaguely remembered that the magnetic pole is somewhere in Canada and that maybe declination was a bigger deal here than it was near London.
So off to the ever helpful Google which took me to http://magnetic-declination.com/ which told me that the declination at Montreal was 14 degrees west while that at London was near enough zero, rather less than it had been when I was a boy scout. But one had to be careful not to click on the large blue buttons which were designed to display full screen advertisements rather than to help.
And so to wikipedia just to confirm my understanding of this matter, where I was pleased to find their article illustrated with a compass very like the one I had just bought, only different in that they had used the A-1000 model rather than the A-10 model. They also had a very natty animated diagram which showed how declination had changed across the world over time - the amount of change over time being far larger than I had expected and the manner of change over space being surprising.
I was reminded of the very similar diagrams of amphidromic points, but with these being to do with tides rather than compasses. See http://pumpkinstrokemarrow.blogspot.ca/search?q=amphidromic. Alternatively, I can ask google about 'amphidromic points. Defined in the 1987 Manual of Navigation' to get to the same place. I suspect google of knowing who is using this PC and tweaking the result accordingly - but it is clever all the same.
I have also learned that I can reference individual posts in volume 1 of this blog, which I had not realised was possible, thinking that its basic unit was the month rather than the post. So http://pumpkinstrokemarrow.blogspot.ca/2011/10/water.html does the job too. I suppose it ought to have been obvious that there was just one database underpinning the whole business, without regard to which template one happened to be using - but it wasn't.
No comments:
Post a Comment